ISNAN

Elemental Intrinsic Function (Generic): Tests whether IEEE* real (S_floating, T_floating, and X_floating) numbers are Not-a-Number (NaN) values.

result = ISNAN (x)

x	(Input) Must be of type real.

Results

The result type is default logical. The result is .TRUE. if x is an IEEE NaN; otherwise, the result is .FALSE..

  LOGICAL A
  DOUBLE PRECISION B
  ...
  A = ISNAN(B)

A is assigned the value .TRUE. if B is an IEEE NaN; otherwise, the value assigned is .FALSE..