MATLAB

About MATLAB

MATLAB is a numerical computing environment and programming language. Created by The MathWorks, MATLAB allows easy matrix manipulation, plotting of functions and data, implementation of algorithms, creation of user interfaces, and interfacing with programs in other languages. Although it specializes in numerical computing, an optional toolbox interfaces with the Maple symbolic engine, making it a full computer algebra system. It is used by more than one million people in industry and academia and runs on most modern operating systems, including Windows, Mac OS, Linux and Unix. The current version is MATLAB 7.1 Service Pack 3. It is available for commercial use for approximately US$2000 and US$100 for an academic license with a limited set of Toolboxes.
— from Wikipedia:MATLAB

For Bioinformatics and Systems Biology, there are useful toolboxes available:

• SBMLToolbox v2.0.2, by the SBML Team download from sourceforge
• SimBiology 1, from Mathworks
• Bioinformatics Toolbox v2.2, from Mathworks

Elementary Tutorial

The following is an unstructured quick bare bones introduction to some of MATLAB's important commands/functions. MATLAB is reasonably easy to use and intuitive to pick up, so go ahead and experiment and learn!

GENERAL COMMANDS

clc

clears the command window

clear

removes all variables from the workspace

clear all

removes all variables, globals, functions and MEX links

ls

Returns listing of the current directory (works on Windows as well)

!ls

Use ! to run shell commands both in windows and linux. In windows, !explorer . maybe a useful command, to browse the current directory

pwd

Shows the present working directory (in Windows too)

help <command name>

gives a brief documentation

doc <command name>

gives the complete documentation

lookfor <text>

looks for the string <text> in the first comment line of the HELP text in all M-files (MATLAB functions/scripts) found on MATLABPATH.

whos

It lists all the variables in the current workspace, together with information about their size, bytes, class, etc.

whos -file <filename.mat>

lists the variables in the specified .MAT file.

type <filename>

'cats' or echoes the file to the screen

ESSENTIAL FUNCTIONS

size

returns the size of the matrix

length

returns the maximum dimension of a matrix

A'

transposes a matrix

1:7:100

Generates numbers upto 100 beginning from 1 in steps of 7.

   >> 1:7:100
   
   ans =
   
        1     8    15    22    29    36    43    50    57    64    71    78    85    92    99
   
   >>   

linspace

linspace(a,b,n) generates n linearly spaced points between a and b

logspace

generates logarithmically spaced points

:

: (colon) is a wildcard (similar to * in shell). e.g. A(:,4:end). This returns all rows of A and columns from 4 onwards. end is a keyword that tells MATLAB to take elements untill the last column is reached.

Entering a vector

x= [1 2 3 4 5]

Entering a matrix

I_4= [1 0 0 0; 0 1 0 0 ; 0 0 1 0; 0 0 0 1] Instead of a semi-colon, line-breaks (Enter) will also work.

A([1 3 5 7],[2 4 6 8])

any submatrix can be addressed; it can even be assigned a value. For example A([1 3 5 7],[2 4 6 8])=0 sets those elements to zero!

prod(size(x))

a simple construct for calculating the number of elements in x.

find(A)

returns the indices of the non-zero elements in a vector. For matrices, it is better to give two outputs: [i,j]=find(A).

sqrt(i)

complex variables are handled seamlessly. i and j are both square roots of -1. Avoid i,j in loops, therefore.

inline

Can create functions like [math]\displaystyle{ f(x,y)=\sin(x^2+y^2+xy) }[/math]. e.g.:

   >> f=inline('sin(x.^2+y.^2+x.*y)')
   
   f =
   
        Inline function:
        f(x,y) = sin(x.^2+y.^2+x.*y)

sparse

Use whenever memory problems are possible due to the usage of large matrices. MATLAB intelligently applies the corresponding algorithms. Typically, just saying A=sparse(A) may cause your code to run 10 times faster, if your matrix is large and sparse.

SPECIAL MATRICES

ones(m,n[,p,..])

Generates a matrix of the corresponding size with all elements 1.

zeros(m,n)

Generates a matrix filled with zeroes; useful for initialisation some times.

rand(n)

gives an n-by-n matrix with random entries, chosen from a uniform distribution on the interval (0.0,1.0).

eye(n)

eye(n) is the n-by-n identity matrix.

eye(m,n)

is an m-by-n matrix with 1's on the diagonal and zeros elsewhere.

Note that a single argument usually creates a square matrix for the above functions.

diag

Can be used to extract the diagonal of a matrix or even create diagonal matrices.