isinf tests for infinite elements

## Syntax

                r = isinf(x)

## Arguments

x

  matrix of real or complex numbers, or of polynomials with real or complex coefficients.

r

  matrix of booleans of the same size as `x`.

## Description

`x` are real or complex numbers: `r = isinf(x)` returns the matrix `r` of booleans such that `r(i)` is `%T` if `abs(x(i))` is infinite, and `%F` otherwise.

`x` are polynomials with real or complex coefficients: Then after `r = isinf(x)`, `r(i)` is `%T` if at least one of the `x(i)` coefficients is infinite, and `%F` otherwise.

## Examples

With real and complex numbers:

    [i, inf, nan] = (%i, %inf, %nan);
    isinf([-1  0.01 -inf  inf  nan])
    isinf([2+i, -10-inf, inf+i])
    isinf([nan-i, nan+i*inf])
    isinf(inf-nan*i)

    --> isinf([-1  0.01 -inf  inf  nan])
     ans  =
      F F T T F

    --> isinf([2+i, -10-inf, inf+i])
     ans  =
      F T T

    --> isinf([nan-i, nan+i*inf])
     ans  =
      F T

    --> isinf(inf-nan*i)
     ans  =
      F

Please note that `%inf-%nan*%i` is computed as `%inf - %nan*complex(0,1) == %inf - complex(%nan*0, %nan*1) == %inf - complex(%nan, %nan) == complex(%inf-%nan, -%nan) == complex(%nan, %nan)` , where Inf is eaten by Nan and no longer appears.

With polynomials :

    p = poly([%nan -2 0 3],"x","coeff")
    q = poly([0 %inf %i],"x","coeff")
    r = poly([%nan %inf*%i 1],"x","coeff")
    isinf([p q r])

    --> p = poly([%nan -2 0 3],"x","coeff")
     p  =
      Nan -2x +3x³

    --> q = poly([0 %inf %i],"x","coeff")
     q  =
      Infx +ix²

    --> r = poly([%nan %inf*%i 1],"x","coeff")
     r  =
      Nan -(Nan-Infi)x +x²

    --> isinf([p q r])
     ans  =
      F T F

## See also

- percentinf
- isnan
- isreal
- isnum
- type

## History

6.1.0 Extension to polynomials.