|GNU Octave Manual Version 3|
by John W. Eaton, David Bateman, Søren Hauberg
Paperback (6"x9"), 568 pages
RRP £24.95 ($39.95)
8.5.1 Element-by-element Boolean Operators
An element-by-element boolean expression is a combination of comparison expressions using the boolean operators “or” (‘|’), “and” (‘&’), and “not” (‘!’), along with parentheses to control nesting. The truth of the boolean expression is computed by combining the truth values of the corresponding elements of the component expressions. A value is considered to be false if it is zero, and true otherwise.
Element-by-element boolean expressions can be used wherever comparison
expressions can be used. They can be used in
statements. However, a matrix value used as the condition in an
while statement is only true if all of its
elements are nonzero.
Like comparison operations, each element of an element-by-element boolean expression also has a numeric value (1 if true, 0 if false) that comes into play if the result of the boolean expression is stored in a variable, or used in arithmetic.
Here are descriptions of the three element-by-element boolean operators.
boolean1 & boolean2
- Elements of the result are true if both corresponding elements of boolean1 and boolean2 are true.
boolean1 | boolean2
- Elements of the result are true if either of the corresponding elements of boolean1 or boolean2 is true.
- Each element of the result is true if the corresponding element of boolean is false.
For matrix operands, these operators work on an element-by-element basis. For example, the expression
[1, 0; 0, 1] & [1, 0; 2, 3]
returns a two by two identity matrix.
For the binary operators, the dimensions of the operands must conform if both are matrices. If one of the operands is a scalar and the other a matrix, the operator is applied to the scalar and each element of the matrix.
For the binary element-by-element boolean operators, both subexpressions boolean1 and boolean2 are evaluated before computing the result. This can make a difference when the expressions have side effects. For example, in the expression
a & b++
the value of the variable b is incremented even if the variable a is zero.
This behavior is necessary for the boolean operators to work as described for matrix-valued operands.
|ISBN 095461206X||GNU Octave Manual Version 3||See the print edition|