Difference between revisions of "MatlabIntro"

Revision as of 12:30, 22 September 2010

Basics

• Use semi-colon at the end of the line to prevent the output of the operation to be printed to the screen

>> x = 1

x =

     1

vs.

>> x = 1;
>>

• Comments are specified using % at the beginning of the comment. Only line comments are allowed (sorry, but no block-comments, although there's a shortcut in the editor to comment out all the selected lines)

>> % This is a comment
>> x = 0; % this is another comment

• Functions may return more than one value, and they can be of any type. For example:

>> [r,c] = size([ones(2)])

r =

     2


c =

     2

Vector and Matrices

• Use square brackets to define a vector/matrix

>> x = [1 2 3 4 5]

• Inside a vector/matrix definition, commas or spaces separate elements row-wise. For example:

>> x = [1 2 3 4 5]

is the same as:

>> x = [1,2,3,4,5]

and they both generate a row vector. Semi-colons, instead, separate elements column-wise. For example, the following line will create a column vector:

>> x = [1;2;3;4;5]

• You can combine both to create a bigger matrix:

>> x = [1 2 3 4;2 3 4 5;3 4 5 6]

x =

     1     2     3     4
     2     3     4     5
     3     4     5     6

• Some useful vector/matrix operators are:

In the following code snippets I'll assume that x was defined as:

>> x = [1 2;3 4]

x =

     1     2
     3     4

• • Use ' as a suffix to transpose the vector/matrix:

>> x'

ans =

     1     3
     2     4
>> 

• • The function size(x) will return the size of x: first number is the number of row and the second is the number of columns:

>> size(x)

ans =

     2     2

• • You can access individual elements of a matrix using parenthesis (first argument specifies the row and the second specifies the column):

>> x(2,1)

ans =

     3

Plotting

The basic command is plot(x), to plot the contents of x (if x is a matrix, then each column is plotted as a different line):

>> fs = 441000;
>> t = 0:1/fs:0.01;
>> plot(sin(2*pi*220*t));

You can also use plot(x,y):

>> plot(t, sin(2*pi*220*t));

By default plot will erase the previous plot before drawing the new one. Use hold to prevent this from happening. Also, you can use a third argument to specify the line color (and other plotting options):

>> hold on;
>> plot(t, sin(2*pi*110*t), 'r');
>> plot(t, sin(2*pi*330*t), 'g');
>> plot(t, sin(2*pi*440*t), 'k');

Sound

General tips

1. Try to vectorize every operation if you can