(octave.info)Logical Values

---

Next: Promotion and Demotion of Data Types Prev: Bit Manipulations Up: Numeric Data Types

---

Enter node , (file) or (file)node

4.6 Logical Values
==================

Octave has built-in support for logical values, i.e., variables that are
either ‘true’ or ‘false’.  When comparing two variables, the result will
be a logical value whose value depends on whether or not the comparison
is true.

   The basic logical operations are ‘&’, ‘|’, and ‘!’, which correspond
to “Logical And”, “Logical Or”, and “Logical Negation”.  These
operations all follow the usual rules of logic.

   It is also possible to use logical values as part of standard
numerical calculations.  In this case ‘true’ is converted to ‘1’, and
‘false’ to 0, both represented using double precision floating point
numbers.  So, the result of ‘true*22 - false/6’ is ‘22’.

   Logical values can also be used to index matrices and cell arrays.
When indexing with a logical array the result will be a vector
containing the values corresponding to ‘true’ parts of the logical
array.  The following example illustrates this.

     data = [ 1, 2; 3, 4 ];
     idx = (data <= 2);
     data(idx)
          ⇒ ans = [ 1; 2 ]

Instead of creating the ‘idx’ array it is possible to replace
‘data(idx)’ with ‘data( data <= 2 )’ in the above code.

   Logical values can also be constructed by casting numeric objects to
logical values, or by using the ‘true’ or ‘false’ functions.

 -- : logical (X)
     Convert the numeric object X to logical type.

     Any nonzero values will be converted to true (1) while zero values
     will be converted to false (0).  The non-numeric value NaN cannot
     be converted and will produce an error.

     Compatibility Note: Octave accepts complex values as input, whereas
     MATLAB issues an error.

     See also: Note: double, Note: single, Note:
     char.

 -- : true (X)
 -- : true (N, M)
 -- : true (N, M, K, ...)
     Return a matrix or N-dimensional array whose elements are all
     logical 1.

     If invoked with a single scalar integer argument, return a square
     matrix of the specified size.

     If invoked with two or more scalar integer arguments, or a vector
     of integer values, return an array with given dimensions.

     See also: Note: false.

 -- : false (X)
 -- : false (N, M)
 -- : false (N, M, K, ...)
     Return a matrix or N-dimensional array whose elements are all
     logical 0.

     If invoked with a single scalar integer argument, return a square
     matrix of the specified size.

     If invoked with two or more scalar integer arguments, or a vector
     of integer values, return an array with given dimensions.

     See also: Note: true.