# Matlab Basics by lr8cj8E

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```									 Matlab Basics

FIN285a: Lecture 2.1
Fall 2010
Grifths Web Notes
Matlab
machine
matlab programs and data from the
website
Matlab Basics
Math Operations
Variables
Vectors
Functions
Fancy subscripts
Program files
Math Operations
Super calculator
+,-,*,/,^, ()
Variables
x=1
1+x
x = 10
y = 20
x*y
The importance of ; (no printing)
x = 1;
Vectors
In matlab variables can be vectors
Vector = list of numbers
x = [1 5 2 1 5];
2*x
x+1
Generating Vectors
: operator
1:10
1:2:10
60:-1:35
x = 1:5;
Parts of Vectors
x(2)
x(10)
x(b)
x(10:15), x(20:end)
Vector Operations
(dot operators)
x = [1 2 3];
y = [ 2 1 3];
x .* y
x ./ y
x .^ y
Matrices
x = [1 2 3; 4 5 6];

x= 1 2 3
4 5 6

rows = 2, columns = 3
Parts of Matrices
x= 1 2 3
4 5 6
x(row, column)
x(2,1) = 4
x(2,:) = 4 5 6
x(1,1:2) = 1 2
Functions
Scalar functions: f(x)
log(x), exp(x), sqrt(x)
sin(x), cos(x), tan(x)

Vector functions
sum(x), mean(x), median(x)
More Functions
plot(x)
plot(x,'*');
Most important function!!!!
Help
help functionname
help plot
Even More Functions
zeros(m,n) : returns a matrix of zeros
ones(m,n) : returns a matrix of ones
rand(m,n) : returns a matrix of uniform
[0,1] random numbers
randn(m,n) : returns a matrix of normal,
mean 0, variance 1, random numbers
(Note: We will often use my own function
Programs (mfiles)
Execute commands in a file
filename.m
Edit using matlab editor (colors)
Examples:
Conditions
>, <, >=, <=, ==, ~=

x>5
x < 10
If conditions
if (x>1)
x = x/2;
end
If/else
if (x<0)
x = x+1;
else
x = -1*x;
end
For loops
for j = [1 2 3]
x(j) = j+1;
end
For Loops
for j = 1:10
x(j) = 2^j;
end

also
x = 2.^(1:10);
For Loops
Useful for dealing with arrays
Costly in terms of computer time
While Loops
x = 20;
y = 0;
while (x>3)
y = y+sqrt(x);
x = x-5;
end
If’s With Vectors
if (a==b)
disp(‘a equals b’)
end

What if a and b are vectors?
True if every element of a equals every
element of b
If’s With Vectors
if (a~=b)
disp(‘a not equals b’)
end

True if every element of a is not equal
Any and All
if any(a==b)
disp(‘at least one equal’)
end

if all(a==b)
disp(‘all are equal’)
end
For matrices this gets more complicated
Fancy Subscripts (find
function)
x = [5 2 -3 -4 1];
y = x(find(x<0));

all x values less than zero put in y
k = find(x<0);
k = subscripts
k = [ 3 4];
Fancy Subscripts
x = [5 2 -3 -4 1];
y = x(x<0);
all x values less than zero put in y
k = x<0;
k = [0 0 1 1 0];
y = x(k) = [-3 -4]
s = sum(k) = 2
Important: Comment Lines
Lines starting with % are comments

x = 1;
y = 2;
z = x*y;
% this really is not doing very much
Getting and Storing Results

diary filename
(all results to filename)
diary off
(stop)
File x.dat =
123
456

Same thing in matrix x
x file must be matrix
Save
save
(saves everything to file matlab.mat)
(restores all settings)
useful for taking a break, and starting
where you left off
Save
save filename x y z
(save to filename.mat variables x, y, z)

save filename x y z -ascii
(save in ascii format)
User Functions
Very important and powerful
Function file (positives.m)
function count = positives(x)
% usage: count = positives(x)
% x = vector
% count = number greater than zero
count = sum(x>0);
Fancy function stuff
Multiple returns

function [ count, count2] = positives(x)
count = sum(x>0);
count2 = sum(x>2);
Summary
We will see many more of these matlab
related commands as we make use of
them

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