REAL function, the `KIND=' value of the type being that of argument X.
REAL; scalar; INTENT(IN).
Intrinsic groups: (standard FORTRAN 77).
Returns the common logarithm (base 10) of X, which must be greater than zero.
The inverse of this function is `10. ** LOG10(X)'.
See Log Intrinsic, for the natural logarithm function.