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# isnan

check for "Not a Number" entries

### Syntax

r=isnan(x)

### Arguments

- x
real or complex vector or matrix r : boolean vector or matrix

### Description

`isnan(x)`

returns a boolean vector or matrix which
contains true entries corresponding with "Not a Number"
`x`

entries and false entries corresponding with regular
`x`

entries.

In this paragraph, we give the reason of the existence of this function.
Consider the floating point number `x`

and assume that
we want to know if this number is a Not A Number.
The condition `(x==%nan)`

is false if `x`

is equal
to `%nan`

. This is why the function `isnan`

is helpful: it allows to
see if a floating point number is a NaN, without actually comparing its value
against `%nan`

.

### Examples

isnan([1 0.01 -%nan %inf-%inf])

In the following example, we see that `%nan`

has very particular
comparison properties and compare the result with the `isnan`

function.

%nan == %nan %nan <> %nan isnan(%nan)

In the following example, we extract the non-NaNs values `y`

from the array `x`

.

x = [1 2 %nan 3 %nan 4] k = find(~isnan(x)) y = x(k)

### See also

- isinf — tests for infinite elements

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