Matlab Commands

ls, pwd, cd, etc.

usual Linux/Windows commands. To execute a shell command, precede it with an exclamation mark.
For example !date (note that Matlab's date has a different result than the Linux command).

computation time

to obtain the time spent doing operations expression, issue it as tic; expression; toc.

unsorted commands

• clc: clear command window
• clear x,y ; clear all: clear some/all variables

Arrays

create/initialize matrices

zeros, ones, eye, diag, rand, randn, magic, etc.

size, length

array dimensions

reshape

change the way an array is arranged as a matrix

' and .'

complex conjugate and transpose, respectively only transpose, a matrix; see the help for transpose

linspace, logspace, meshgrid, etc.

produces an array of values, in one to three dimensions

Strings

• strings in Matlab are determined by simple quotation marks, e.g. 'Peter'
• to include the quotation mark in the string, it has to be doubled (e.g., the string Peter's is defined as 'Peter''s')
• for example, try in Matlab:

  	  
  	    mystring='Peter''s'
  	    mystring
  	  
  	

• to include variable values in a string, can do e.g.

  	  
  	    M=100
  	    ['the current value of M is ', num2str(M)]
  	  
  	

• see help strings for more

Graphing

printing a graph (from octave)

if there are no mouse options/buttons can try (see How do I create a plot without a window popping up (ie, a plot to a file)?; link correct as of 2014.11)

• method said to work only with gnuplot as graphics_toolkit;
• plot the graph;
• then, e.g, print -dpdf "file.pdf"

figure

creates a new figure window, or brings the focus to the one specified. See also clf clear current figure window, gcf current figure handle (into which graphics commands like plot will draw), etc.; see the help and doc for figure

close

close windows

cla, clf

clear axes, clear figure

graph ingredients

the appearance of a graph can be adjusted either from the menus in its window, or with axis, box, xlabel, ylabel, title, legend, text, gtext, etc. The strings used in these allow TeX-like commands, for example
title('\bf Graph of \beta=\alpha_1+\alpha_{21}^3')
There are many more parameters (do get(H), where H is the handle to a figure; e.g., get(gcf) are the parameters of the current figure).
To change these parameters, use set(H, 'property1', 'value1', 'property2', 'value2', etc.). For example, set(gcf, 'name', 'Sine curves') sets the name of the current window.

subplot

puts separate graphs (axes) in the same window

ezplot, ezsurf, etc.

easy versions of the plotting commands; do lookfor easy for more such commands

fplot

plots a function on a given interval. E.g., fplot(@humps,[0 1]), fplot(@(x) sin(1./x), [0.01 0.1], 1e-3); see more in help fplot

plot

Plots functions of one variable.
Also plot3, semilogx, semilogy, loglog, plotyy, etc.; see the help for plot

Other graphical representations: bar, barh, stairs, stem, pie, hist, polar, etc.
See also fplot.

surf

Plots a function of two variables.
It can be used as surf(x,y,z) with z a matrix of size n x m and

• either x a vector of size n and y a vector of size m
• or x and y matrices of size n x m.

Also surfc, surfl, contour, contour3, mesh, meshz, meshc, bar3, etc.; see the help for surf
Here is an example:

		    
[X,Y]=meshgrid(linspace(1,2,10), linspace(3,5,10));

gr=mesh(X,Y,X+Y-6,'edgecolor','green')
hold on
bl=mesh(X,Y,2*X-Y,'edgecolor','black')
alpha(gr, .5)
alpha(bl, .5)
		      
		  

The value of alpha, between 0 and 1, measures the transparency: 0=totally transparent, 1=totally opaque. See more at "help alpha".

Programming

which

Locate functions and files; it can have more arguments.
For example, which FUN1 in FUN2 displays the pathname to function FUN1 in the context of the m-file FUN2.

type

list the content of an M-file
This is an alternative to opening the file in a text-editor, after finding its location with which

if, for, while, switch/case, break, continue, return, etc.

the usual program control commands; see help matlab/lang

error

issue an error message and abort the function

eval(expression)

Evaluates a string as a Matlab expression
For example, eval(['x' '+' 'y']) is the same as x+y.

Note: it seems (but did not find documentation for this behaviour) that one can call eval with two parameters, both strings, eval(string1, string2); if the evaluation of the first string fails, the second is evaluated, if that also fails an error message is issued.
This is useful to check whether the evaluation of the first string was successful (instead of a try - catch block). Below is an example:

		    
>> eval('u*')
??? Error: Expression or statement is incomplete or incorrect.
 
>> eval('u*','3')

ans = 3

>> eval('u*','3+')
??? Error: Expression or statement is incomplete or incorrect.
 
>> test=0; eval('u+v+', 'test=1')

test = 1
		    
		  

So, in a program, where say 'input_string' is a string provided by the user, can do

		    
test=0;
eval('result=input_string','test=1');
if test==1
  % this means that eval('result=input_string') has failed
  %	so do something else
.....
end
% otherwise, continue using  result as planned
.....
		    
		  

feval(F,x1,...,xn)

Evaluates the function specified by a function handle or function name, F, at the given arguments, x1,...,xn.
For example, if F = @foo, then feval(F,9.64) or feval('foo',9.64) is the same as foo(9.64).
This is useful, e.g., if you want to pass to a subroutine a function as a parameter.

function

define a function in an M-file
by default, variables in a function M-file are local

A few related Matlab objects (check the Matlab documentation for a more precise description):

mfilename

name of currently executing M-file (as a string)

nargin

number of arguments in the function's actual call

nargout

number of function output arguments

varargin

variable length input argument list (a cell array); allows any number of arguments to a function

varargout

variable length output argument list (a cell array); allows any number of output arguments from a function

global

make a variable global

I/O, files

load

load data (or variables, if they were saved with save)

format

Change the precision used to display the results. It has many options.
E.g.,

• format long to have more digits
• format rat to give a rational approximation
• format short (or just format) to return to the default, about five significant digits
• etc.

fprintf

formated printing (similar to C); see the help, but more information is given in doc fprintf.

For example, fprintf('the values are: x = %5.2f, n = %i\n',x,n)

fopen, fclose

open/close files to read, write, append

disp

displays an array, without printing the array name

input

prompt for user input

type

list the content of an M-file

Various other commands

quad, quadl, trapz

numerical integration

round, floor, ceil, fix

roundings to integers

roots

find the roots of a polynomial (by computing the eigenvalues of the companion matrix)

fzero

find zero of a function

eig

compute eigenvalues and eigenvectors of a matrix

ode45

Integrate a vector-valued ODE, giving the vector-field, the initial condition etc. ("45" refers to the algorithm used).

dfield and pplane

these were developed by John C. Polking from Rice University
updated versions of these are at http://math.rice.edu/~dfield/

dfield plots integral curves (click on Proceed, then click in the window) for a scalar ODE, x'=f(x,t).
pplane plots integral curves (click on Proceed, then click in the window) for a system x'=f(x,y), y'=g(x,y).

There are many more features.

curve fitting

see "Basic fitting" in the "Tools" menu of a figure