[GiNaC-devel] Patches to fix nonnegative info flag

[Vladimir V. Kisil]

	Dear All,

	I am attaching three micro patches to fix problems with the
  following programme (present output is included):

#include "ginac/ginac.h"

int main(){
	GiNaC::ex half=GiNaC::numeric(1,2),
		E=-pow(8, half);

	std::cout << "E nonneg: " << E.info(GiNaC::info_flags::nonnegative) << std::endl;
	// --> E nonneg: 1

	std::cout << "Absolute value of E: " << abs(E) << std::endl;
	// --> Absolute value of E: -sqrt(8)

	std::cout << "Absolute value of (-E): " << abs(-E) << std::endl;
	// --> Absolute value of (-E): abs(sqrt(8))

	return 0;
}

  First, the present GiNaC returns
  mul::info(GiNaC::info_flags::nonnegative) just opposite to the correct
  one. This is one patch.

  Second, presently pow::info(GiNaC::info_flags::nonnegative) can be
  false even if pow::info(GiNaC::info_flags::positive) is true. this the
  second patch.

  Finally, I think that abs shall return -arg if arg is negative or
  (-arg) is nonnegative, this is the third patch.

  If all three patches are implemented, then the output of the above
  example is:

E nonneg: 0
Absolute value of E: sqrt(8)
Absolute value of (-E): sqrt(8)

  Best wishes,
  Vladimir
-- 
Vladimir V. Kisil                 http://www.maths.leeds.ac.uk/~kisilv/
  Book:     Geometry of Mobius Transformations     http://goo.gl/EaG2Vu
  Software: Geometry of cycles          http://moebinv.sourceforge.net/
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