tests if a string represents a number
res = isnum(str)
a character string or a matrix of character strings.
a boolean matrix.
res = isnum(str)
returns %t
if
str
represents a number.
isnum
does not handle "operations", but only pure scalar numbers.
For instance, isnum("1+2*3")
will return %f
.
Complex numbers are not concerned, because one complex number is defined by the addition of two parts.