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Subsections

EXIST Text Existence of a Variable

Usage

Tests for the existence of a variable. The general syntax for its use is

  y = exist('varname')

The return is 1 if a variable with the name varname exists in the current workspace and is not empty. This function is primarily useful when keywords are used in function arguments.

Example

Some examples of the exist function. Note that generally exist is used in functions to test for keywords. For example,

  function y = testfunc(a, b, c)
  if (~exist('c'))
    % c was not defined, so establish a default
    c = 13;
  end
  y = a + b + c;

An example of exist in action.

--> a = randn(3,5,2)
a = 
  <double>  - size: [3 5 2]
(:,:,1) = 
 
Columns 1 to 2
   -0.0361639933961680       -0.238187257168569      
   -0.140415140955028         0.599755385896831      
    0.693389551907565         0.708649351074680      
 
Columns 3 to 4
   -0.939406097470966        -0.164794584325194      
   -0.00648807006806828       0.0101167556598398     
   -0.0530953547548948        0.160105749424486      
 
Columns 5 to 5
   -1.465385481298682      
   -0.0395884566172688     
    1.182465366442761      
(:,:,2) = 
 
Columns 1 to 2
   -0.744595958059576        -1.029772319457510      
    0.647296600570314         0.691289627813676      
   -0.403233868578614        -0.513911033581514      
 
Columns 3 to 4
   -0.625280812142897         0.747620555277489      
   -0.121927486686842        -0.844868680099879      
    0.502771253977369         0.438758894856345      
 
Columns 5 to 5
   -0.567515585636787      
    0.840068850555420      
   -1.266240568477841      
--> b = []
b = 
  <double>  - size: []
  []
--> who
  Variable Name      Type   Flags   Size
              a    double           [3 5 2]
              b    double           []
            ans    double           []
--> exist('a')
ans = 
  <logical>  - size: [1 1]
 1  
--> exist('b')
ans = 
  <logical>  - size: [1 1]
 0  
--> exist('c')
ans = 
  <logical>  - size: [1 1]
 0



2004-10-27