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					   Chapter 5
Advanced Plotting
and Model Building
Matlab, Maple & Mathematica – plots are part of the
package!!!

Type help graph2d       or graph3d to get help
Anatomy of a typical xy (2D) plot. Figure 5.1–1
Scale on axis – range and spacing
of the numbers.
Here both axis are linear (later will
see logarithmic…).

More? See
pages 260-
5-2                                                    261.
The following MATLAB session plots y = 0.4 1.8x for 0  x
 52, where y represents the height of a rocket after
launch, in miles, and x is the horizontal (downrange)
distance in miles.

>>x = [0:0.1:52]; % create vector of finely spaced pts
>>y = 0.4*sqrt(1.8*x); % to produce a smooth curve
>>plot(x,y)
>>xlabel(’Distance (miles)’)
>>ylabel(’Height (miles)’)
>>title([‘Rocket Height as a Function of
Downrange Distance’,num2str(dist)])

The resulting plot is shown on the next slide.

5-3
The autoscaling feature in MATLAB selects tick-mark
spacing. Figure 5.1–2

5-4
The plot will appear in the Figure window.
You can obtain a hard copy of the plot in several ways:

1. Use the menu system. Select Print on the File menu in
the Figure window.
Answer OK when you are prompted to continue the
printing process.
2. Type print at the command line.
This command sends the current plot directly to the
printer.
3. Save the plot to a file to be printed later or imported into
another application such as a word processor.
You need to know something about graphics file formats
to use this file properly.
See the subsection Exporting Figures.

5-5
Note that using the Alt-Tab key combination in Windows-
based systems will return you to the Command window
without closing the figure window.

If you do not close the window, it will not reappear when a
new plot command is executed.
However, the figure will still be updated.

5-6
Requirements for a Correct Plot

The following list describes the essential features of any plot:

1. Each axis must be labeled with the name of the quantity
being plotted and its units!
If two or more quantities having different units are plotted
(such as when plotting both speed and distance versus
time), indicate the units in the axis label if there is room, or
in the legend or labels for each curve.

2. Each axis should have regularly spaced tick marks at
convenient intervals — not too sparse, but not too dense —
with a spacing that is easy to interpret and interpolate.
For example, use 0.1, 0.2, and so on, rather than 0.13,
0.26, and so on.

5-7
(continued …)
Requirements for a Correct Plot (continued)

3. If you are plotting more than one curve or data set, label each
on its plot or use a legend to distinguish them.

4. If you are preparing multiple plots of a similar type or if the
axes’ labels cannot convey enough information, use a title.

5. If you are plotting measured data, plot each data point with a
symbol such as a circle, square, or cross (use the same
symbol for every point in the same data set).
If there are many data points, plot them using the dot symbol.

(continued …)
5-8
Requirements for a Correct Plot (continued)

6. Sometimes data symbols are connected by lines to
help the viewer visualize the data, especially if
there are few data points.
However, connecting the data points, especially
with a solid line, might be interpreted to imply
knowledge of what occurs between the data points.
Thus you should be careful to prevent such
misinterpretation.

7. If you are plotting points generated by evaluating a
function (as opposed to measured data), do not
use a symbol to plot the points.
Instead, be sure to generate many points, and
connect the points with solid lines.
5-9
The grid and axis Commands

The grid command displays gridlines at the tick marks corresponding to the tick
labels.
Type grid on to add gridlines;
type grid off to stop plotting gridlines.

You can use the axis command to override the MATLAB selections for the axis limits.
The basic syntax is axis([xmin xmax ymin ymax]).
This command sets the scaling for the x- and y-axes to the minimum and maximum
values indicated.
Note that, unlike an array, this command does not use commas to separate the values.

axis square, equal, auto

5-10
More? See pages 264-265.
The effects of the axis and grid commands. Figure 5.1–3

5-11
Plot of Complex numbers
The plot(y) function plots the values in y versus the indices.
However, if y is complex plot(y) plots the imaginary parts vs real parts, i.e.
plot( real(y) , imag(y) )
In all other variants of the plot function, it ignores the imaginary parts.

Example:
z = 0.3 + 0.7*i
0.6
n = [0:0.001:100];
plot(z.^n)
0.4
xlabel('Real')
ylabel('Imaginary')
Imaginary

0.2
axis equal

0

-0.2

-0.4
-0.4   -0.2   0   0.2      0.4   0.6   0.8   1
Real

5-12
The fplot – smart command for plotting functions - plots function specified as string.
It automatically analyzes the function to pick proper spacing, so that plot will show all
the features of the function – adaptive plotting.
Syntax is fplot(‘string’,[xmin xmax ymin ymax])

[x,y] = fplot(‘cos(tan(x)) – tan(sin(x))’,[1,2]) - automatically
picked denser points in the more complicated region

5-13
Contrast the previous plot with:
x = [1:0.01:2];
y = cos(tan(x)) – tan(sin(x));
plot(x,y) – much less detailed

Another form is [x,y]=fplot(‘string’,limits) – returns abscissa and ordinate values
in the column vectors x and y, but no plot is produced.
The returned values can be used for plotting multiple curves etc…

5-14
Plotting Polynomials with the polyval Function.

To plot the polynomial 2x5– 4x3 + 2x2 + 10 over the range –4  x 
4 with a spacing of 0.01, you type

>>x = [-4:0.01:4];                            % setting the spacing
>>p = [2,0,-4,2,0,10];            % setting the coefficients
>>plot(x,polyval(p,x))
>>xlabel(’x’)
>>ylabel(’p’)                         50

40

30

20
p

10

0

-10       More? See page 268.
-20
-2   -1.5   -1   -0.5   0   0.5   1   1.5   2
5-15                                                             x
An example of a Figure window. Figure 5.1–7

5-16
Saving Figures

To save a figure that can be opened in subsequent
MATLAB sessions, save it in a figure file with the .fig
file name extension.

To do this, select Save from the Figure window File
menu or click the Save button (the disk icon) on the
toolbar.

If this is the first time you are saving the file, the Save
As dialog box appears.
Make sure that the type is MATLAB Figure (*.fig).
Specify the name you want assigned to the figure file.
Click OK.

5-17
Exporting Figures

To save the figure in a format that can be used by another application, such
as the standard graphics file formats TIFF or EPS, perform these steps:

1. Select Export Setup from the File menu.
This dialog lets you specify options for the output file, such as the figure
size, fonts, line size and style, and output format.

2. Select Export from the Export Setup dialog.
A standard Save As dialog appears.

3. Select the format from the list of formats in the Save As type menu.
This selects the format of the exported file and adds the standard file
name extension given to files of that type.

4. Enter the name you want to give the file, less the extension. Then click
Save.

5-18                                      More? See pages 270-271.
On Windows systems, you can also copy a figure to
the clipboard and then paste it into another
application:

1. Select Copy Options from the Edit menu. The
Copying Options page of the Preferences
dialog box appears.

2. Complete the fields on the Copying Options
page and click OK.

3. Select Copy Figure from the Edit menu.

5-19
Subplots
Matlab can create array of rectangular panes – subplots.

The syntax is subplot(m,n,p).

This command divides the Figure window into an array of
rectangular panes with m rows and n columns.

The variable p tells MATLAB to place the output of the plot
command following the subplot command into the pth pane.

For example, subplot(3,2,5) creates an array of six panes,
three panes deep and two panes across, and directs the next
plot to appear in the fifth pane (in the bottom-left corner).

5-20
The following script file created Figure 5.2–1, which shows
the plots of the functions y = e-1.2x sin(10x + 5) for 0  x  5
and y = |x3 - 100| for -6  x  6.

x = [0:0.01:5];
y = exp(-1.2*x).*sin(10*x+5);
subplot(1,2,1)
plot(x,y),axis([0 5 -1 1])

x = [-6:0.01:6];
y = abs(x.^3-100);
subplot(1,2,2)
plot(x,y),axis([-6 6 0 350])

The figure is shown
on the next slide.
5-21
Application of the subplot command. Figure 5.2–1

More on
subplots?
See page
271.

5-22
Overlay Plots                6
y1
Simple Overlay:              5
y2

4
x = -1:0.01:2;
3
y1 = x.^2 - 1;
2
y2 = x.^3 - 2;               1

plot(x,y1,x,y2)              0

legend('y1','y2')           -1

-2

-3
-1   -0.5   0   0.5   1   1.5   2

Matrix Overlays:
plot(A) plots the columns of A vs indices and generates n curves where A is matrix with m rows
and m columns.
plot(x,A) plots the matrix A vs the vector x, where x is either a row vector or column vector and
A is a matrix with m rows and n columns.
If the length of x is m, then each column of A is plotted vs vector x
If the length of x is n , then each row       of A is plotted vs vector x
plot(A,x) plots the vector x vs the matrix A
If the length of x is m, then x is plotted vs each column of A
If the length of x is n , then x is plotted vs each row      of A
plot(A,B) plots columns of the matrix B vs columns of the matrix A
Data Markers and Line Types

To plot y versus x with a solid line and u versus v with
a dashed line, type plot(x,y,u,v,’--’), where the
symbols ’--’ represent a dashed line.

Table 5.2–1 gives the symbols for other line types.

To plot y versus x with asterisks (*) connected with a
dotted line:
plot(x,y,’*:’).

5-23
To plot y versus x with green asterisks (*) connected
with a red dashed line, you must plot the data twice by
typing plot(x,y,’g*’,x,y,’r--’).

5-24
Specifiers for data markers, line types, and colors.
Table 5.2–1
Data markers†                  Line types                      Colors

Dot (.)                   .    Solid line             ––       Black        k
Asterisk (*)              *    Dashed line            ––       Blue         b
Cross ()                     Dash-dotted line       –.       Cyan         c
Circle ( )                     Dotted line            ….       Green        g
Plus sign (+)             +                                    Magenta      m
Square ( )                s                                    Red          r
Diamond ( )               d                                    White        w
Five-pointed star (w)     p                                    Yellow       y
†Other   data markers are available. Search for “markers” in MATLAB help.

Useful when you plot many different data types on the same plot

5-26
We can plot two different sets of data on the
same plot with:
3

x1 = -1:0.1:2;                                             y1
y2

x2 = 0 :0.1:1.5;         2

y1 = -x1.^2 + 1;
y2 = x2.^3 - 1;          1

plot(x1,y1,x2,y2,'*:')
legend('y1','y2')        0

-1

-2

-3
-1   -0.5   0   0.5   1   1.5        2
Use of data markers. Figure 5.2–2

More?
See
pages
273-274.

5-27
Labeling Curves and Data

The legend command automatically obtains from
the plot the line type used for each data set and
displays a sample of this line type in the legend
box next to the string you selected.

The following script file produced the plot in Figure
5.2–4.

x = [0:0.01:2];
y = sinh(x);
z = tanh(x);
plot(x,y,x,z,’--’),xlabel(’x’), ...
ylabel(’Hyperbolic Sine and
Tangent’), ...
legend(’sinh(x)’,’tanh(x)’)
5-28
Application of the legend command. Figure 5.2–4

5-29
The gtext and text commands are also useful. Figure 5.2–5
Another way to distinguish graphs is to
place text next to each one.

GTEXT('string') displays the graph
window, puts up a cross-hair, and waits
for a mouse button or keyboard key to
be pressed.
The cross-hair can be positioned with
the mouse (or with the arrow keys on
some computers).
Pressing a mouse button or any key
writes the text string onto the graph at
the selected location.

Example
gtext({‘first line','second line'})

gtext({'First line','Second
line'},'FontName','Times','Fontsize',12)

There is also text(x,y,’string’), but here
you have to specify x and y coordinates
5-30                          in advance.
Graphical solution of equations:
To get a first guess on solution of two equations in two unknowns, plot the equations.
Solution is at the intersection of two lines.
If they do not intersect – no solutions, if multiple intersections – multiple solutions.

Example:
Circuit representation of a power supply and a load. Example 5.2-1. Figure 5.2–6

5-31
Plot of the load line and the device curve for Example 5.2–1.
Figure 5.2–7

5-32
Application of the hold command. Figure 5.2–8
hold – holds the figure still allowing to add more plots later.

HOLD ON holds the current plot and all axis
x = -1:0.01:1;                   properties so that subsequent graphing
y1 = 3 + exp(-x).*sin(6*x);
y2 = 4 + exp(-x).*cos(6*x);      commands add to the existing graph.
z = 0.1 + 0.9*i ;
n = 0:0.01:10;                   HOLD OFF returns to the default mode whereby
plot(z.^n)
hold on
plot(y1,y2)                      PLOT commands erase the previous plots and
hold off                         reset all axis properties before drawing new
plots.

It is not really needed in many cases because we
can plot multiple graphs with
plot(x,y,x,z,’--’), but useful here
because plots are of different types and also
useful for advanced toolboxes.

5-33
Hints for Improving Plots

The following actions, while not required, can nevertheless
improve the appearance of your plots:

1. Start scales from zero whenever possible.
This technique prevents a false impression of the
magnitudes of any variations shown on the plot.

2. Use sensible tick-mark spacing.
If the quantities are months, choose a spacing of 12
because 1/10 of a year is not a convenient division.
Space tick marks as close as is useful, but no closer.
If the data is given monthly over a range of 24 months, 48
tick marks might be too dense, and also unnecessary.

(continued …)
5-34
Hints for Improving Plots (continued)
3. Minimize the number of zeros in the data being plotted.
For example, use a scale in millions of dollars when
appropriate, instead of a scale in dollars with six zeros after
every number.

4. Determine the minimum and maximum data values for each
axis before plotting the data.
Then set the axis limits to cover the entire data range plus
an additional amount to allow convenient tick-mark spacing
to be selected.

For example, if the data on the x-axis ranges from 1.2 to
9.6, a good choice for axis limits is 0 to 10.
This choice allows you to use a tick spacing of 1 or 2.

5-35                                                  (continued …)
Hints for Improving Plots (continued)

5. Use a different line type for each curve when several are plotted on a
single plot and they cross each other;
for example, use a solid line, a dashed line, and combinations of lines
and symbols.
Beware of using colors to distinguish plots if you are going to make
black-and-white printouts and photocopies.

6. Do not put many curves on one plot, particularly if they will be close to
each other or cross one another at several points.

7. Use the same scale limits and tick spacing on each plot if you need to
compare information on more than one plot.

Note:
Matlab can create text, titles, and labels using Math symbols in TEX
title(‘A e^{-t/\tau)sin(\omega t)’) backslash \ must precede each TEX
character sequence.

5-36
Why use log scales?
1) To represent graphs that cover wide ranges.
2) To identify certain trends in data, because some types of functional relationships
appear as straight lines when plotted using log scale.
In the example below we have wide variation in both abscissa and ordinate, so loglog
plot is much more useful.

5-37
Logarithmic Plots

It is important to remember the following points when
using log scales:

1) You cannot plot negative numbers on a log scale,
because the logarithm of a negative number is not
defined as a real number.

2) You cannot plot the number 0 on a log scale,
because log10 0 = ln 0 = -.
You must choose an appropriately small number as
the lower limit on the plot.
(may just rescale your data to start with 1)

(continued…)
5-39
Logarithmic Plots (continued)
3) The tick-mark labels on a log scale are the actual values being plotted;
they are not the logarithms of the numbers.
For example, the range of x values in the plot in Figure 5.3–2 is from 10-1 = 0.1 to 102 =
100.

4) Equal distances on a log scale correspond to multiplication by the same constant (as opposed
to addition of the same constant on a rectilinear scale). log(a*b) = log(a) + log(b)

For example, all numbers that differ by a factor of 10 are separated by the same distance on a
log scale.
That is, the distance between 0.3 and 3 is the same as the distance between 30 and 300.
This separation is referred to as a decade or cycle.

Gridlines and tick marks within a decade are unevenly spaced.
If 8 gridlines or tick marks occur within the decade, they correspond to values equal to 2, 3, 4, .
. . , 8, 9 times the value represented by the first gridline or tick mark of the decade.

(continued…)
5-40
Logarithmic Plots (continued)

The plot shown in Figure 5.3–2 covers three decades
in x (from 0.1 to 100) and four decades in y and is
thus called a four-by-three-cycle plot.

5-41
MATLAB has 3 commands for generating plots having log scales.
The appropriate command depends on which axis must have a log scale.

1. Use the loglog(x,y) command to have both scales logarithmic.

2. Use the semilogx(x,y) command to have the x scale logarithmic and
the y scale rectilinear.

3. Use the semilogy(x,y) command to have the y scale logarithmic and
the x scale rectilinear.

5-42
Two data sets plotted on four types of plots. Figure 5.3–3
x1 = 1:0.2:3;
y1 = 3*x1.^2;                                  70                                 70
y2 = 3*exp(x1);                                                      power
y3 = 3*log(x1)                                 60                    exp          60

subplot( 2, 2, 1)                                                    log
50                                 50
plot(x1,y1,'d-.',x1,y2,'*-',x1,y3,'o:')
legend('power','exp','log')                    40                                 40
grid on
subplot( 2, 2, 2)                              30                                 30

semilogx(x1,y1,'d-.',x1,y2,'*-',x1,y3,'o:')
20                                 20
grid on
%legend('power','exp','log')                   10                                 10
subplot( 2, 2, 3)
semilogy(x1,y1,'d-.',x1,y2,'*-',x1,y3,'o:')        0
1   1.5   2    2.5    3
0
0
10
grid on
%legend('power','exp','log')
subplot( 2, 2, 4)
loglog(x1,y1,'d-.',x1,y2,'*-',x1,y3,'o:')      2
10
2
10
grid on
%legend('power','exp','log')

1                                  1
10                                 10
y1 – power dependence is linear only
on log log plot
y2 - exp is linear only on semilogy            0
10
0
10

y3 - log is linear only on semilogx
-1                                 -1
10                                 10
1   1.5   2    2.5    3          0
10
Application of logarithmic plots: An RC circuit. Figure 5.3–4

Frequency-response plot of a low-pass RC circuit.
Figure 5.3–5

RC = 0.1;
s = [ 1:100 ] * i;
M = abs(1./(RC*s+1));
loglog(imag(s),M)

At omega about 10 rad/sec the amplitude
of any signal with freq greater than this
one, will decrease by more than 30%
=> low pass filter
An example of controlling the tick-mark labels with the set
command. Figure 5.3–6

Changes tick marks
from numbers to
text labels of months

See
pages
287-289.

set(gca,’XTicklabel’,[‘Jan’; ‘Feb’   ])
set(gca,’XTick’,[1:6])
Specialized plot commands. Table 5.3–1

Command                 Description

bar(x,y)                Creates a bar chart of y versus x.

plotyy(x1,y1,x2,y2)     Produces a plot with two y-axes, y1
on the left and y2 on the right.

polar(theta,r,’type’)   Produces a polar plot from the polar
coordinates theta and r, using the
line type, data marker, and colors
specified in the string type.

stairs(x,y)             Produces a stairs plot of y versus x.

stem(x,y)               Produces a stem plot of y versus x.

5-43
A polar plot showing an orbit around Sun (at the origin) having an
eccentricity of 0.5.

Polar plot r = r(theta) – very
hard to do by hand!!!

theta = linspace(0, 2*pi,100);
r = 2 ./ (1 – 0.5*cos(theta)/2);
polar(theta,r)

Class: T5.3-1 and 3, p291

See pages
290-291.

5-48
Interactive Plotting in MATLAB

This interface can be advantageous in situations where:

 You need to create a large number of different types of
plots,

 You must construct plots involving many data sets,

 You want to add annotations such as rectangles and
ellipses, or

 You want to change plot characteristics such as tick
spacing, fonts, bolding, italics, and colors.

More? See pages 292-298.
5-49
The interactive plotting environment in MATLAB is a set of
tools for:

 Creating different types of graphs,

 Selecting variables to plot directly from the Workspace
Browser,

 Creating and editing subplots,

 Adding annotations such as lines, arrows, text,
rectangles, and ellipses, and

 Editing properties of graphics objects, such as their color,
line weight, and font.

5-50
The Figure window with the Figure toolbar displayed.
Figure 5.4–1

5-51
The Figure window with the Figure and Plot Edit toolbars
displayed. Figure 5.4–2

5-52
The Plot Tools interface includes the following three
panels associated with a given figure.

 The Figure Palette: Use this to create and arrange
subplots, to view and plot workspace variables, and to
add annotations.

 The Plot Browser: Use this to select and control the
visibility of the axes or graphics objects plotted in the
figure, and to add data for plotting.

 The Property Editor: Use this to set basic properties
of the selected object and to obtain access to all
properties through the Property Inspector.

5-53
The Figure window with the Plot Tools activated.
Figure 5.4–3

Note that we can capture
all the changes made
to the plot by
File-> Generate M-file

5-54
Function Discovery. The power function y = 2x -0.5 and the
exponential function y = 101-x . Figure 5.3–8

5-55
8                                         8
linear
7                       power             7
My example:                                     6
10x
6

5                                         5
x = linspace(0.1,2,10);
y1 = 1 + 0.5*x;                                 4                                         4
y2 = 2*x.^2;
y3 = 10.^(0.3*(1+x))                            3                                         3
subplot( 2, 2, 1)
2                                         2
plot(x,y1,'d-.',x,y2,'*-',x,y3,'o:')
legend('linear','power','10^x')
1                                         1
grid on
subplot( 2, 2, 2)                               0                                         0
semilogx(x,y1,'d-.',x,y2,'*-',x,y3,'o:')            0   0.5   1   1.5            2        10
-1      0
10
1
10
grid on
subplot( 2, 2, 3)
semilogy(x,y1,'d-.',x,y2,'*-',x,y3,'o:')
grid on
1                                         1
subplot( 2, 2, 4)                          10                                        10
loglog(x,y1,'d-.',x,y2,'*-',x,y3,'o:')
grid on

0                                         0
10                                        10

-1                                        -1
10                                        10

-2                                        -2
10                                        10
0   0.5   1   1.5            2            -1    0    1
10       10   10
Using the Linear, Power, and Exponential Functions
to Describe data.

Each function gives a straight line when plotted using a
specific set of axes:

1. The linear function y = mx + b gives a straight line
when plotted on rectilinear axes.
Its slope is m and its intercept is b.

2. The power function y = bxm gives a straight line when
plotted on log-log axes.

3. The exponential function y = b(10)mx and its
equivalent form y = bemx give a straight line when
plotted on a semilog plot whose y-axis is logarithmic.
More? See pages 299-300.
5-56
Steps for Function Discovery
Summary of the procedures to find a function that describes a given set of data:
Assume one of the function types - linear, exp, or power - can describe the data.

1.    Examine the data near the origin.
The exponential function y = b*10^(mx) can never pass through the origin

The linear function y = m*x + b can pass through the origin only if b = 0.

The power function y = b*x^m can pass through the origin but only if m > 0.

5-57
Steps for Function Discovery (continued)

2. Plot the data using rectilinear scales.

If it forms a straight line, then it can be represented by the
linear function and you are finished.

Otherwise, if you have data at x = 0, then
a. If y(0) = 0, try the power function.
b. If y(0)  0, try the exponential function.

If data is not given for x = 0, proceed to step 3.

5-60
Steps for Function Discovery (continued)

3. If you suspect a power function, plot the data using log-log
scales.

Only a power function will form a straight line on a log-log plot.

If you suspect an exponential function, plot the data using the
semilog scales.

Only an exponential function will form a straight line on a
semilog plot.

(continued…)
5-61
Steps for Function Discovery (continued)

4. In function discovery applications, we use the log-log
and semilog plots only to identify the function type, but
NOT to find the coefficients b and m.

The reason is that it is difficult to interpolate on log scales
and we can do it much better on the linear scales.

5-62
The polyfit function. Table 5.5–1

Command               Description

p =                   Fits a polynomial of degree n to
polyfit(x,y,n)        data described by the vectors x and
y, where x is the independent
variable.

Returns a row vector p of length n
+ 1 that contains the polynomial
coefficients in order of descending
powers.

5-63
Using the polyfit Function to Fit Equations to
Data.

Syntax: p = polyfit(x,y,n)

where x and y contain the data, n is the order of the
polynomial to be fitted, and p is the vector of
polynomial coefficients.

The linear function: y = mx + b.
In this case the variables w and z in the polynomial w
= p1z+ p2 are the original data variables x and y, and
we can find the linear function that fits the data by
typing p = polyfit(x,y,1).
The first element p1 of the vector p will be m, and the
second element p2 will be b.
5-64
The power function: y = bxm. In this case

log10 y = m log10x + log10b           (5.5–5)

which has the form
w = p1z + p2

where the polynomial variables w and z are related to the
original data variables x and y by w = log10 y and z = log10x.
Thus we can find the power function that fits the data by
typing

p = polyfit(log10(x),log10(y),1)

The first element p1 of the vector p will be m, and the
second element p2 will be log10b. We can find b from b =
10p2 .
5-65
The exponential function: y = b(10)mx. In this case

log10 y = mx + log10b              (5.5–6)

which has the form
w = p1z + p2

where the polynomial variables w and z are related to the
original data variables x and y by w = log10 y and z = x. We
can find the exponential function that fits the data by typing

p = polyfit(x, log10(y),1)

The first element p1 of the vector p will be m, and the
second element p2 will be log10b. We can find b from b =
10p2 .
5-66                               More? See pages 302-303.
clear all; clf;
disp('--------------------------------')
My Example
x = [ 5, 10:10:100 ];                               Stretch of a spring data
y = [ 0 19 57 94 134 173 216 256 297 343   390 ];
Fitting line
p = polyfit(x,y,1)                                                                D = 4.1596 dmax = 8.4741
xv = linspace(min(x),max(x),1000);                    400

yv = polyval(p,xv);
200

residuals = y - polyval(p,x);                           0

dmax = max(abs(residuals))
D = sqrt( sum(residuals.^2) / length(x))              -200
0       10    20    30      40       50       60   70    80   90   100

Residuals
subplot(2,1,1)                                         10

plot(x,y,'o',xv,yv)                                     5

grid on                                                 0
title(['D = ',num2str(D),‘…
-5
dmax = ',num2str(dmax)])
-10
0       10    20    30      40       50       60   70    80   90   100

subplot(2,1,2)
plot(x,residuals,'*:')
grid on                                                                               D = 1.1087 dmax = 2.4567
title('Residuals')                                      400

300

%Fitting line                                           200

p = 4.0693 *x -25.4071                                  100

0
0    10    20   30       40       50      60    70   80   90   100

%Fitting quadratic, just make it polyfit(x,y,2):             2
Residuals

p = 0.0049*x^2 + 3.5629*x -17.1145                           0

-2

-4
0    10    20   30       40       50      60    70   80   90   100
Fitting a linear equation: An experiment to measure force and
deflection in a cantilever beam. Example 5.5-1.
Figure 5.5–3

5-67
Plots for the cantilever beam example. Figure 5.5–4

5-68
clear all; clf;
disp('--------------------------------')

x = [ 0:100:800 ];
y = [ 0 0.09 0.18 0.28 0.37 0.46 0.55 0.65 0.74];

p = polyfit(x,y,1)
xv = linspace(min(x),max(x),1000);
yv = polyval(p,xv);                                                          Note that the book actually plots
k = 1/p(1)                                                                   just x = f/k, not the full polynomial.
residuals = y - polyval(p,x);
dmax = max(abs(residuals))
D = sqrt( sum(residuals.^2) / length(x))

subplot(2,1,1)
plot(x,y,'o',xv,yv)
D = 0.0026294 dmax = 0.0042222
grid on                                                        1
title(['D = ',num2str(D),' dmax =
',num2str(dmax)])

Deflection
0.5
xlabel('Force'); ylabel('Deflection');
0
subplot(2,1,2)
plot(x,residuals,'*:')
-0.5
grid on                                                             0        100   200    300      400      500   600   700   800
title('Residuals')                                                      -3
Force
x 10                        Residuals
5

p=    0.0009*x - 0.0018
0

k = 1/(p(1) = 1079.1 lb/inch     ( f = k*x )
-5
0        100   200    300      400      500   600   700   800
clear all; clf;                                               Fitting an exponential function.
disp('--------------------------------')
Temperature of a cooling cup of coffee,
x = [ 0 620 2262 3482 ];
y = [ 145 130 103 90 ];
plotted on various coordinates.
y = y - 68; % subtract room temperature

subplot(2,2,1)
plot(x,y,'o-')
xlabel('Time (sec)');   ylabel('Relative Temperature (F)');

subplot(2,2,2)
semilogy(x,y,'o-')
xlabel('Time (sec)');   ylabel('Relative Temperature (F)');

p = polyfit(x,log10(y),1)
m = p(1)
b = 10^p(2)
xv = linspace(min(x),max(x),1000);
yv = b*10.^(m*xv);

t120 = (log10(120-68) - log10(b))/ m ;
80

Relative Temperature (F)

Relative Temperature (F)
subplot(2,2,3)                                                                                                                                                              1.8
10
semilogy(xv,yv+68,x,y+68,'o',t120,120,'*')
60
xlabel('Time (sec)'); ylabel('Relative Temperature (F)');
1.6
10
subplot(2,2,4)                                                                                      40
plot(xv,yv+68,x,y+68,'o',t120,120,'*')                                                                                                                                      1.4
xlabel('Time (sec)'); ylabel('Relative Temperature (F)');                                                                                                                  10
20
0   1000 2000 3000   4000                                                0   1000 2000 3000   4000
Time (sec)                                                               Time (sec)

p = -0.0002 x + 1.8889                                                                               3
10                                                                     160
Relative Temperature (F)

Relative Temperature (F)
m = -1.5563e-004                                                                                                                                                           140

b = 77.4361                                                                                          2
10                                                                     120

100

The model is T – 68 = b*10^(m*t)                                                                     1
10
0   1000 2000 3000   4000
80
0   1000 2000 3000   4000
Time (sec)                                                               Time (sec)
Fitting an exponential function. Temperature of a cooling cup
of coffee, plotted on various coordinates. Example 5.5-2.
Figure 5.5–5

5-69
Fitting a power function. An experiment to verify Torricelli’s
principle. Example 5.5-3. Figure 5.5–6

5-70
x = [ 6:3:15 ];
times = [ 9 8 7 6];
flow = 1./times;
y = flow;

p = polyfit(log10(x),log10(y),1)
m = p(1)
b = 10^p(2)
xv = linspace(min(x),max(x),1000);
yv = b*xv.^m;

subplot(2,1,1)
loglog(xv,yv,x,y,'o')
xlabel('Volume (cups)');   ylabel('Flow Rate (cups/sec)');
axis('tight')

subplot(2,1,2)
plot(xv,1./yv,x,1./y,'o')
xlabel('Volume (cups)'); ylabel('Fill time (sec)');
axis('tight')

Flow Rate (cups/sec)
disp('Extrapolation:')                                                                    -0.7
10
V = 36
f36 = b*V^m                                                                   10
-0.8

filltime = 1/f36                                                                          -0.9
10
----------------------------------------------------
1
p = 0.4331*x - 1.3019                                                                                    10
Volume (cups)
m = 0.4331
b = 0.0499                                                                                      9

8
Fill time (sec)

Extrapolation:                                                                                  7
6
V = 36                                                                                          5
f36 = 0.2356
filltime = 4.2452                                                                                   10   15   20       25     30   35   40
Volume (cups)
Flow rate and fill time for a coffee pot. Figure 5.5–7

5-71
The Least Squares Criterion: used to fit a function f (x).
It minimizes the sum of the squares of the residuals, J.
J is defined as

m
J =    S    [ f (xi ) – yi ]2   (5.6–1)
i=1

We can use this criterion to compare the quality of the
curve fit for two or more functions used to describe the
same data. The function that gives the smallest J value
gives the best fit.

5-72
Illustration of the least squares criterion. Figure 5.6–1

5-73
The least squares fit for the example data. Figure 5.6–2

See pages
312-315.
5-74
My Example of Linear Fit:
clear all; clf;
x = [ 0 3 8]
y = [ 1 4 10]

p = polyfit(x,y,1)

pval = polyval(p,x)
J = sum( ( pval - y ).^2 )            10

xvec = linspace(min(x),max(x),100);   9

yvec = polyval(p,xvec);               8
plot(xvec,yvec,x,y,'o')
7

6
--------------------------------      5

p = 1.1327 0.8469                     4

pval = 0.8469 4.2449 9.9082           3

J = 0.0918                            2

1

0
0   1   2   3   4   5   6   7   8
The polyfit function is based on the least-squares
method. Its syntax is

p =                  Fits a polynomial of degree n to
polyfit(x,y,n)       data described by the vectors x
and y, where x is the independent
variable.

Returns a row vector p of length
n+1 that contains the polynomial
coefficients in order of descending
powers.

See page 315, Table 5.6-1.

5-75
Regression using polynomials of first through fourth degree.
Figure 5.6–3

The program
is on pages
315 to 316.

5-76
My Example from polyfit
% Improving code on p 315 and changing data
clear all; clf;
x = -2:10;
y = -2+3*x + 5*exp(0.3*x);
xp = linspace( min(x), max(x),1000);
for k = 1:4 % power of polynomials
Polyn deg = 1       J = 2048.368                  Polyn deg = 2       J = 179.9441
coeff = polyfit(x,y,k);
120                                               120
yp = polyval(coeff,xp);
100                                               100
J = sum( (polyval(coeff,x) - y).^2 );
subplot(2,2,k)                                  80                                                80

plot(xp,yp,x,y,'o');                            60                                                60

x

x
axis ([ min(x)-0.2 max(x)+0.2 ...               40                                                40

min(y)-0.2 max(y)+0.2 ])               20                                                20
xlabel('x'); ylabel('x');                        0                                                 0
title(['Polyn deg = ',num2str(k),...                   0                   5             10              0                   5             10
x                                                 x
'     J = ',num2str(J)])
Polyn deg = 3       J = 8.9246                   Polyn deg = 4       J = 0.27338
end
120                                               120
100                                               100

80                                                80

60                                                60
x

x
40                                                40

20                                                20

0                                                 0
0                   5             10              0                   5             10
x                                                 x
Beware of using polynomials of high degree. An example of
a fifth-degree polynomial that passes through all six data
points but exhibits large excursions between points. Figure
5.6–4

5-77
My example, exact polynomial
fit of high degree.
% p 317 exact polyn fit of high degree
clear all; clf;
x = 0:6;                                      4
Polyn deg = 3   J = 11.7413
3
Polyn deg = 4       J = 10.2753

y = -4+8*rand(size(x));
2
xp = linspace( min(x), max(x),1000);          2
for k = 3:6 % power of polynomials                                                           1

coeff = polyfit(x,y,k);                     0                                              0

x

x
yp = polyval(coeff,xp);                                                                    -1
-2
J = sum( (polyval(coeff,x) - y).^2 );                                                      -2
subplot(2,2,k-2)                            -4                                             -3
0         2            4          6            0           2                4           6
plot(xp,yp,x,y,'o');                                             x                                                  x
%axis ([ min(x)-0.2 max(x)+0.2 ...                   Polyn deg = 5   J = 4.6253                     Polyn deg = 6       J = 9.784e-024
%        min(y)-0.2 max(y)+0.2 ])           4                                              4

xlabel('x'); ylabel('x');                                                                  2
2
title(['Polyn deg = ',num2str(k),...
0
'    J = ',num2str(J)])              0
x

x
end                                                                                          -2
-2
-4

-4                                             -6
0         2            4          6            0           2                4           6
x                                                  x
Assessing the Quality of a Curve Fit:

Denote the sum of the squares of the deviation of
the y values from their mean y by S, which can be
computed from      m
S=   S     (yt – y )2      (5.6–2)
i=1

5-78
This formula can be used to compute another measure of
the quality of the curve fit, the coefficient of determination,
also known as the r-squared value. It is defined as

r2= 1- J                       (5.6–3)
S

The value of S indicates how much the data is spread
around the mean, and the value of J indicates how
much of the data spread is unaccounted for by the
model.

Thus the ratio J / S indicates the fractional variation
unaccounted for by the model.

5-79
For a perfect fit, J = 0 and thus r 2 = 1. Thus the closer
r 2 is to 1, the better the fit. The largest r 2 can be is 1.

It is possible for J to be larger than S, and thus it is
possible for r 2 to be negative. Such cases, however,
are indicative of a very poor model that should not be
used.

As a rule of thumb, a good fit accounts for at least 99
percent of the data variation. This value corresponds
to r 2  0.99.

More? See pages 319-320.

5-80
Quality of Curve Fit (my example)

% p 319 Curve fitting example
clear all; clf;
x = -2:10;
y = -2+3*x + 2*sin(x);
ym = mean(y);
xp = linspace( min(x), max(x),1000);      Deg = 1; J = 24.5642; S = 1764.7432; r2 = 0.98608   Deg = 2; J = 23.0771; S = 1764.7432; r2 = 0.98692
30                                                  30
for k = 1:4 % power of polynomials
coeff = polyfit(x,y,k);                     20                                                  20
yp = polyval(coeff,xp);
J = sum( (polyval(coeff,x) - y).^2 );       10                                                  10

x

x
S = sum( (y - ym).^2 );
0                                                   0
r2 = 1 - J/S;
subplot(2,2,k)                              -10                                                 -10
plot(xp,yp,x,y,'o');                           -5        0
x
5            10              -5        0
x
5            10

%axis ([ min(x)-0.2 max(x)+0.2 ...
Deg = 3; J = 22.0227; S = 1764.7432; r2 = 0.98752   Deg = 4; J = 12.6007; S = 1764.7432; r2 = 0.99286
%        min(y)-0.2 max(y)+0.2 ])        30                                                  30
xlabel('x'); ylabel('x');
20
title(['Deg = ',num2str(k),...              20

'; J = ',num2str(J)...                                                                   10
10
x

x
'; S = ',num2str(S)...                                                                     0
'; r^2 = ',num2str(r2)])               0
-10
end
-10                                                 -20
-5        0            5            10              -5        0            5            10
x                                                   x
Scaling the Data

The effect of computational errors in computing the
coefficients can be lessened by properly scaling the
x values. You can scale the data yourself before
using polyfit. Some common scaling methods
are

1. Subtract the minimum x value or the mean x value
from the x data, if the range of x is small, or

2. Divide the x values by the maximum value or the
mean value, if the range is large.

More? See pages 323-324.

5-81
Effect of coefficient accuracy on a sixth-degree polynomial.
Top graph: 14 decimal-place accuracy. Bottom graph: 8
decimal-place accuracy. Figure 5.6–5

More? See
pages 320-
321.
5-82
Avoiding high degree polynomials: Use of two cubics to fit
data. Figure 5.6–6

See
pages
321-
322.
5-83
x = [ 1990:1999 ];
y= [ 2.1 3.4 4.5 5.3 6.2 6.6 6.8 7 7.4 7.8];
Example 5.6.1
p = polyfit(x,y,3)
Estimation of Traffic Flow
Warning: Polynomial is badly conditioned. Add points with distinct X
values, reduce the degree of the polynomial, or try centering
and scaling as described in HELP POLYFIT.

clear all; clf;
subtract off initial year
disp('--------------------------------')
J = sum(   (polyval(coeff,x) - y).^2 );
x = [ 1990:1999 ] - 1990;                                                                              S = sum(   (y - ym).^2 );
y= [ 2.1 3.4 4.5 5.3 6.2 6.6 6.8 7 7.4 7.8];                                                           r2 = 1 -   J/S;
Get r2 =   0.9972 – very good!

p = polyfit(x,y,3)

xv = linspace(min(x),max(x),1000);
7
yv = polyval(p,xv);

Cars (millions)
6

subplot(2,1,1)                                                                                     5

plot(xv,yv,x,y,'o')                                                                                4

xlabel('year'); ylabel('Cars (millions)');                                                         3

axis('tight')                                                                                      0       1      2    3    4       5      6   7   8   9
year
residuals = y - polyval(p,x);                                                                                               Residuals
subplot(2,1,2)
plot(x,residuals,'o:')
Cars (millions)

0.1
xlabel('year'); ylabel('Cars (millions)');
axis('tight')                                                                                      0
title('Residuals')
-0.1
p=    0.0087(x -1990)^3 - 0.1851(x-1990)^2 +                                                           0   1      2    3    4          5   6   7   8   9
1.5991(x – 1990) + 2.0362                                                                                                 year
Traffic Flow
clear all; clf;
disp('--------------------------------')
Alternative approach using mu
x = [ 1990:1999 ] ;
y= [ 2.1 3.4 4.5 5.3 6.2 6.6 6.8 7 7.4 7.8];

[p,s,mu] = polyfit(x,y,3)                                               Using s and mu to center the polynomial
around average of x and its
xv = linspace(min(x),max(x),1000);
yv = polyval(p,xv,s,mu);                                                standard deviation mu = [ aver std ]
subplot(2,1,1)
plot(xv,yv,x,y,'o')
xlabel('year'); ylabel('Cars (millions)');
axis('tight')

residuals = y - polyval(p,x,s,mu);                                                  7
subplot(2,1,2)

Cars (millions)
6
plot(x,residuals,'o:')
5
xlabel('year'); ylabel('Cars (millions)');
4
axis('tight')
3
title('Residuals')
1990   1991   1992   1993   1994    1995   1996   1997   1998   1999
year
Residuals
Cars (millions)

0.1

0

-0.1
1990   1991   1992   1993   1994    1995   1996   1997   1998   1999
year
Using Residuals: Residual plots of four models. Figure 5.6–7

See pages
325-326.

5-84
Linear-in-Parameters Regression: Comparison of first- and
second-order model fits. Figure 5.6–8

See
pages
329-331.

5-85
Basic Fitting Interface

MATLAB supports curve fitting through the Basic Fitting
interface. Using this interface, you can quickly perform
basic curve fitting tasks within the same easy-to-use
environment. The interface is designed so that you can:

 Fit data using a cubic spline or a polynomial up to
degree 10.
 Plot multiple fits simultaneously for a given data set.
 Plot the residuals.
 Examine the numerical results of a fit.
 Interpolate or extrapolate a fit.
 Annotate the plot with the numerical fit results and
the norm of residuals.
 Save the fit and evaluated results to the MATLAB
workspace.
5-86
The Basic Fitting interface. Figure 5.7–1

5-87
A figure produced by the Basic Fitting interface.
Figure 5.7–2

More?
See
pages
5-88                                                331-334.
Applications of interpolation: A plot of temperature data
versus time. Figure 7.4–1

7-32
% P 446 my example
clear all; clf;
% temperature measured every
% 2 hours, but need it every hour
x = 0:2:24;
y = 60 + 20*sin(2*pi*x/24);
xv = linspace( min(x),max(x),1000);
yv = 60 + 20*sin(2*pi*xv/24);
xint = 0:24;
yint = interp1(x,y,xint);
plot(xv,yv,x,y,'o',xint,yint,'*')
80

75

70

65

60

55

50

45

40
0   5   10   15   20   25
Temperature measurements at four locations. Figure 7.4–2

More? See
pages 444-449.
7-33
Linear interpolation functions. Table 7.4–1

Command                     Description

Y_int =                     Used to linearly interpolate
interp1(x,y,x_int)          a function of one variable:
y = f (x).

Returns a linearly
interpolated vector y_int
at the specified value
x_int, using data stored
in x and y.

7-34
Table 7.4–1 Continued

Z_int = interp2(x,y,z,x_int,y_int)

Used to linearly interpolate a function of two
variables: y = f (x, y).

Returns a linearly interpolated vector z_int at the
specified values x_int and y_int, using data stored
in x, y, and z.

7-35
Cubic-spline interpolation:
The following session produces and plots a cubic-spline
fit, using an increment of 0.01 in the x values.

>>x = [7,9,11,12];
>>y = [49,57,71,75];
>>x_int = [7:0.01:12];
>>y_int = spline(x,y,x_int);
>>plot(x,y,’o’,x,y,’--’,x_int,y_int),...
xlabel(’Time (hr)’),ylabel(’Temperature
(deg F)’,...
title(’Temperature Measurements at a
Single Location’),...
axis([7 12 45 80])

This produces the next figure.
7-36
Linear and cubic-spline interpolation of temperature data.
Figure 7.4–3

7-37                               More? See pages 449-452.
% P 451 my example splines
clear all; clf;
disp('-----------------------')
% Just a random set of temperature data
x = 0:2:24;
y = 60 + 20*rand(size(x));
xint = linspace( min(x),max(x),1000);
yint = interp1(x,y,xint,'spline');
plot(x,y,'o',x,y,'-.',xint,yint)
legend('Data','Linear','Cubic Spline')
xtry = [ 12.5 1.5];
ytry = interp1(x,y,xtry,'spline')

ytry = 66.9181 73.1265 -- to get spline approximation at specific points

85

Data
Linear
80           Cubic Spline

75

70

65

60
0   5         10       15   20   25
Polynomial interpolation functions. Table 7.4–2

Command

y_est = interp1(x,y,x_est,’spline’)

Description

Returns a column vector y_est that contains the estimated
values of y that correspond to the x values specified in the
vector x_est, using cubic-spline interpolation.

7-38
Table 7.4–2 Continued

Y_int = spline(x,y,x_int)

Computes a cubic-spline interpolation where x and y are
vectors containing the data and x_int is a vector
containing the values of the independent variable x at which
we wish to estimate the dependent variable y.
The result Y_int is a vector the same size as x_int
containing the interpolated values of y that correspond to
x_int.

7-39
Table 7.4–2 Continued

[breaks, coeffs, m, n] = unmkpp(spline(x,y))

Computes the coefficients of the cubic-spline polynomials for
the data in x and y.

The vector breaks contains the x values, and the matrix
coeffs is an m  n matrix containing the polynomial
coefficients.

The scalars m and n give the dimensions of the matrix
coeffs; m is the number of polynomials, and n is the
number of coefficients for each polynomial.

7-40
My Example for spline coefficients
clear all; clf;
x = [7:7:42]';
y = [8 41 133 250 280 297];
xx = linspace(min(x),max(x),1000);

yy = spline(x,y,xx);
[breaks, coeffs, m, n] = unmkpp(spline(x,y))
plot(x,y,'o',xx,yy)
title('Spline fit')

Spline fit
300

breaks = 7 14 21 28 35 42
250
coeffs =
-0.0004 0.6102 0.4619 8.0000
-0.0004 0.6020 8.9476 41.0000       200

-0.0972 0.5939 17.3190 133.0000
0.0626 -1.4469 11.3476 250.0000    150
0.0626 -0.1327 0.2905 280.0000
m= 5
100
n=     4

50

0
5   10   15   20      25        30   35   40   45
3-D plots
We look at three basic types:
line, surface and contour plots.
Three-Dimensional Line Plots:

>>t = [0:pi/50:10*pi];
>>plot3(exp(-0.05*t).*sin(t),exp(-0.05*t).*cos(t),t),...
xlabel(’x’),ylabel(’y’),zlabel(’z’),grid

t goes from 0 to 10*pi
sin/cos go through 5 cycles
x^2 + y^2 = exp(-0.1t) decreases.
x and y decrease!

5-89
Surface Plots:
z = f(x,y) – represents a surface in 3D.
mesh, surf etc… generate surface plots.

First, need to generate a grid (mesh) of points in x-y plane and evaluate f on it.
x = xmin: dx : xmax; y = ymin: dy : ymax;
[X,Y] = meshgrid(x,y)      generates such a grid with corners (xmin,ymin) and
(xmax,ymax)
Matrices X and Y contain coordinate pairs of every point on the grid

If x and y are the same, can use [X,Y]   = meshgrid(x)

The following session shows how to generate the surface plot of the function
z = xe-[(x-y2)2+y2], for -2 <= x <= 2 and -2 <= y <= 2, with a spacing of 0.1.

This plot appears in Figure 5.8–2.

>>[X,Y] = meshgrid(-2:0.1:2);
>>Z = X.*exp(-((X-Y.^2).^2+Y.^2));
>>mesh(X,Y,Z),xlabel(’x’),ylabel(’y’),zlabel(’z’)

5-91
A plot of the surface z = xe-[(x-y2)2+y2] created with the mesh
function. Figure 5.8–2

More? See pages 335-336.
5-92
My example with surf command:
[X,Y] = meshgrid(-2:0.1:2);
Z = sqrt(X.^2+Y.^2).*exp(-2*((X-Y).^2+Y.^2));
surf(X,Y,Z),xlabel('x'),ylabel('y'),zlabel('z')

0.5

0.4

0.3
z

0.2

0.1

0
2
1                                       2
0                               1
0
-1             -1
y        -2   -2
x
Contour Plots
Topographic plots show the contours of the land by means of
constant elevation lines – contour lines.

The following session generates the contour plot of the function
whose surface plot is shown in Figure 5.8–2;
namely, z = xe-[(x-y2)2+y2], for -2  x  2 and -2  y  2, with a
spacing of 0.1.

>>[X,Y] = meshgrid(-2:0.1:2);
>>Z = X.*exp(-((X- Y.^2).^2+Y.^2));
>>contour(X,Y,Z),xlabel(’x’),ylabel(’y’)

5-93
A contour plot of the surface z = xe-[(x-y2)2+y2] created with the
contour function. Figure 5.8–3

More? See
page 337.

5-94
Three-dimensional plotting functions. Table 5.8–1
Function                  Description
contour(x,y,z)            Creates a contour plot.

mesh(x,y,z)               Creates a 3D mesh surface plot.

meshc(x,y,z)              Same as mesh but draws contours under the
surface.

meshz(x,y,z)              Same as mesh but draws vertical reference lines
under the surface.

surf(x,y,z)               Creates a shaded 3D mesh surface plot.

surfc(x,y,z)              Same as surf but draws contours under the
surface.

[X,Y] = meshgrid(x,y) Creates the matrices X and Y from the vectors x
and y to define a rectangular grid.

[X,Y] = meshgrid(x)       Same as [X,Y]= meshgrid(x,x).

waterfall(x,y,z)          Same as mesh but draws mesh lines in one
5-95                         direction only.
Plots of the surface z = xe-(x2+y2) created with the mesh
function and its variant forms: meshc, meshz, and
waterfall. a) mesh, b) meshc, c) meshz, d) waterfall.
Figure 5.8–4

5-96
The following slides contain
figures from the chapter’s
homework problems.

5-97
Figure P27

5-98
Figure P28

5-99
Figure P56

5-100


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