Log functions as per the Gnu Scientific Library, reference manual
section 7.25 and AMS-55, chapter 4. These functions are declared in
header file gsl_sf_log.h
In complex_log(), the imaginary part of the
argument. If missing (ie takes the default value of NULL),
interpret zr as complex, even if real
r.and.i
In complex_log(), Boolean variable with
default value of TRUE meaning to return a complex variable as
per the details section below; and FALSE meaning to return
the values as advertised in the GSL manual
give
Boolean with TRUE meaning to return a list of three
items: the value, an estimate of the error, and a status number
strict
Boolean, with TRUE meaning to return NaN
if status is an error