Elemental Intrinsic Function (Generic): Tests whether IEEE® real (S_floating and T_floating) numbers are Not-a-Number (NaN) values.
Syntax
Results:
The result is of type default logical. The result is .TRUE. if x is an IEEE NaN; otherwise, the result is .FALSE..
Examples
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..