[GiNaC-list] atan2(0,-4) = -Pi?

[Jan Bos]

Dear All,

Is there a reason for GiNaC (or ginsh) to evaluate 
atan2(0,-4) as -Pi instead of +Pi the definition used by for instance
C/C++? Looking at the code, inifcns_trans.cpp last shown case below,
explicitly states it should. Or can I expect it to be changed in the
future?

static ex atan2_eval(const ex & y, const ex & x)
{
  if (y.info(info_flags::numeric) && x.info(info_flags::numeric)) {

    if (y.is_zero()) {

      // atan(0, 0) -> 0
      if (x.is_zero())
	return _ex0;

      // atan(0, x), x real and positive -> 0
      if (x.info(info_flags::positive))
	return _ex0;

      // atan(0, x), x real and negative -> -Pi
      if (x.info(info_flags::negative))
	return _ex_1*Pi;
    }

...

The code fragment is from version 1.3.7

best regards

Jan Bos