MATLAB Function Reference |
Repeatedly execute statements while condition is true
Syntax
Description
while
repeats statements
an indefinite number of times. The statements
are executed while the real part of expression
has all nonzero elements. expression
is usually of the form
where rel_op
is ==, <, >, <=, >=, or ~=.
The scope of a while
statement is always terminated with a matching end
.
expression
expression
is a MATLAB expression, usually consisting of variables or smaller expressions joined by relational operators (
e.g., count < limit
) or logical functions (e.g., isreal(A)
).
Simple expressions can be combined by logical operators (&
, |
, ~
) into compound expressions such as the following. MATLAB evaluates compound expressions from left to right, adhering to operator precedence rules.
statements
statements
is one or more MATLAB statements to be executed only while the expression
is true
or nonzero.
Nonscalar Expressions
If the evaluated expression
yields a nonscalar value, then every element of this value must be true
or nonzero for the entire expression to be considered true
. For example, the statement while
(A < B)
is true
only if each element of matrix A
is less than its corresponding element in matrix B
. See Example 2, below.
Partial Evaluation of the Expression Argument
Within the context of an if
or while
expression, MATLAB does not necessarily evaluate all parts of a logical expression. In some cases it is possible, and often advantageous, to determine whether an expression is true
or false
through only partial evaluation.
For example, if A
equals zero in statement 1 below, then the expression evaluates to false
, regardless of the value of B
. In this case, there is no need to evaluate B
and MATLAB does not do so. In statement 2, if A
is nonzero, then the expression is true
, regardless of B
. Again, MATLAB does not evaluate the latter part of the expression.
You can use this property to your advantage to cause MATLAB to evaluate a part of an expression only if a preceding part evaluates to the desired state. Here are some examples.
while (b ~= 0) & (a/b > 18.5) if exist('myfun.m') & (myfun(x) >= y) if iscell(A) & all(cellfun('isreal', A))
Example 1 - Simple while Statement
The variable eps
is a tolerance used to determine such things as near singularity and rank. Its initial value is the machine epsilon, the distance from 1.0 to the next largest floating-point number on your machine. Its calculation demonstrates while
loops.
Example 2 - Nonscalar Expression
A = B = 1 0 1 1 2 3 3 4
See Also
end
, for
, break
, continue
, return
, all
, any
, if
, switch
which | whitebg |
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