Tests whether the input is a number.
A series, scalar or string value to test.
An integer, 1 or 0.
If a macro, GAIN, were defined as:
#define gain mean(W1)
returns 1 since gain expands to mean(W1) which evaluates to a scalar.
If the macro, GAIN, were defined as:
#define gain 'mean(W1)'
returns 0 since the macro gain is defined as the string: 'mean(W1)'.
a = 12;
b = "12";
isnumber(a) returns 1.
isnumber(b) returns 0.