Basics

Shortcuts

Use the TAB key to complete commands, file-names, etc.

Use the up and down arrows to select a previous command.
Or, type the first letters of a previous command before using the arrows to select only the matching commands.

Use the left and right keys to edit commands.

Comments

Begin with the percentage sign (%).

Continuation lines

Three or more decimal points (that is,   ...  ) at the end of a line cause the following line to be a continuation.

Suppresing output

The output of a command will not be displayed if the command ends in a semi-colon (;).
E.g.,

x=5, y=1:10; z=7

will display the values of x and z but not that of y (the latter is the array [1 2 3 4 5 6 7 8 9 10]).

Matlab files

The files that contain Matlab commands are called M-files, and have the extension .m (e.g., my_file.m). These can be scripts or functions (see below).
Binary Matlab files have the extension .mat.
Data files (for example, large matrices) have usually the extension .dat.

Executing commands

One can execute commands in various ways.
The last item below is the primary way to define new functions in Matlab.

• type them at the Matlab prompt
• use M-files:
  • script files
    • write the commands (with a text editor) in an M-file and have Matlab read the file in by giving the file name at the prompt (without the .m extension)
      (this is equivalent to the previous approach, except that the commands can be used for another occasion);
    • See the corresponding section in Octave's manual (now 11.10 Script Files).
  • function files
    • define a function in an M-file.
    • The name of the file has to be that of the function, with the .m extension.
      For example, the command   ode45   (used to solve ODE's) is in the file ode45.m. To find where this file is, do which ode45; you can open the file with a text editor to see how the solver is implemented.
    • by defauls, variables used in a function are local; to make them global, use global
    • See the corresponding section in Octave's manual (now 11.9 Function Files).
  • See more details in the section Editing M-files.

Function arguments

Usually the arguments are passed as f(x,y,'string',z); for some functions the parantheses are optional, but then the arguments are seen as strings.

For example title Disk is the same as title('Disk').

Predefined variables

Some of these are also functions, see the help.

• ans is the result of the last computation
• pi is 3.14159265358... (to see more decimals, set format long)
• i and j, or sqrt(-1), the imaginary unit
• eps=epsilon, roughly the smallest distance between two numbers (that is, the available precision)
• Inf=Infinity, NaN=Not a Number
• realmax and realmin, the largest/smallest positive numbers in the given precision (default is double)

Array operations

• Since all Matlab variables are arrays and Matlab is meant to work easily with matrices, operations that have a natural meaning for matrices are understood as such.

  E.g., * denotes multiplication of matrices (if so are the operands; dimensions must match).
  However, 6*[1 2; 3 4] multiplies each entry of the matrix by 6 and 1+[1 2;3 4] adds 1 to each entry.

• To operate entrywise on an array, use the operation preceded by a period.
  E.g., A.^2 squares each entry of the array A, whereas A^2 squares the matrix (if it is not a square matrix, an error is signaled).
  [1 2; 3 4] .* [3 5; 7 9] multiplies entrywise the two matrices; the result is [3 10; 21 36].
• Other functions act by default entrywise.
  E.g., sin([pi/2 pi 3*pi/2]) gives [1 0 -1].
• To compute x sin(x) for an array x=[1 2 3 4] use x .* sin(x).

Listing and removing variables

• who or whos to list current variables
• clear to remove all variables
• clear x, y, matr* to remove certain variables

Saving/loading

Use the commands save and load to save or load variables/data.
Can choose to save the variables in binary format (the default) or as ASCII. The binary files are specific to the Matlab version.
The whole worskpace can be saved at the end of a session (and restored at the beginning of the next).

WARNING:

• By default, save overwrites the file.
• When saving in binary (.mat file) the name of the variable is also included, but when saving in ASCII only the values are.
• Examples:
  • save xyvariables x y % saves x and y in binary to the file xyvariables.mat
    load xyvariables % restores x and y
  • save ~/xvalues x -ascii % save the values of x in the file ~/xvalues.mat
    x=load('~/xvalues') % assign to x its saved values

Recording commands

Use the command diary. Here is most of what help diary says:

 DIARY Save text of MATLAB session.
    DIARY FILENAME causes a copy of all subsequent command window input
    and most of the resulting command window output to be appended to the
    named file.  If no file is specified, the file 'diary' is used.
 
    DIARY OFF suspends it. 
    DIARY ON turns it back on.
    DIARY, by itself, toggles the diary state.
 
    Use the functional form of DIARY, such as DIARY('file'),
    when the file name is stored in a string.