On Tuesday, 26 November 2013 at 11:22:38 UTC, Joseph Rushton
Wakeling wrote:
On 26/11/13 02:02, Andrei Alexandrescu wrote:
If you got the blessing of some complex number expert, that
would be great.
I'm in Italy, I could ask the pope ... :-)
As far as I can see the behaviour of std.complex.Complex is
consistent both with C++'s std::complex and with D's own
internal cfloat/cdouble/creal types. The only case we don't
cover with std.complex is that of multiplying a complex number
with a purely imaginary one (the equivalent of multiplying,
say, a creal and an ireal; multiplying a creal and a creal,
even if the real part of the latter is 0, will give the same
results as std.complex).
We _could_ tweak Complex internally so that in the event that
its real part is 0, it behaves like a purely imaginary number,
and if its imaginary part is 0, it behaves like a purely real
number; but that's problematic for reasons already discussed,
because it doesn't distinguish between a purely imaginary
number versus one where the real part is so vanishingly small
that FP considers it to be 0.
(It also leaves std.complex' behaviour incompatible with
std::complex and other library implementations, though I guess
that's less of a concern so long as we think what std.complex
does is right.)
So, as other people have suggested, really the only thing we
can reasonably do is to define a separate Imaginary type -- or
get round the problems with the built-in complex and imaginary
types. It is really a shame if they are as problematic as I've
heard. :-(
It seems to me that one really shouldn't special case for
absolute values when dealing with floating point. A floating
Imaginary type and an integer Complex type - both in std.complex
- are the correct solutions IMO.
