[Octave-bug-tracker] [bug #43349] asin behaves differently from Matlab for arguments larger than 1

[Rik]

Follow-up Comment #9, bug #43349 (project octave):

I agree that the problem is the conversion of a real to a complex value with
zero for the imaginary unit.  I think the problem is that we use the default
form of the C++ Complex constructor with just a single argument.  The Complex
constructor is shown below 


template<> class complex<double> {
  complex (double re = 0.0, double im = 0.0);


When it is called in rc_asin with just a single argument then the imaginary
unit takes the default which is always +0.0.


   return fabs (x) > 1.0 ? asin (Complex (x)) : Complex (asin (x));


However, if I use the two argument form and explicitly set the phase of the
imaginary unit then I get the correct answer.  The replacement code below
works on the examples in this bug report.


Complex
rc_asin (double x)
{
  return fabs (x) > 1.0 ? asin (Complex (x, signbit (x) ? -0.0 : +0.0))
                        : Complex (asin (x));
}



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