[phobos] Is anyone working on std.complex?

[Don Clugston]

On 25 March 2010 22:54, Andrei Alexandrescu <andrei at erdani.com> wrote:
> Good call! Walter mentioned he should transfer some knowledge to Don in the
> matter. Walter, please let us know how we can plan this.
>
> Don suggested that the polar representation is very seldom used so we may as
> well throw it away.

That's not the direct reason. The issue is that it's difficult to do
polar representation in a way which preserves numerically desirable
properties. For instance, the invariant   if (x==x) assert( x == -
(-x)); MUST be preserved, but isn't true for a naive polar
representation. This rules out the use of floating point for the arg
-- you probably want to use some form of fixed point. Then you have
the problem that PI isn't exactly representable as a floating-point
number. And it's downhill from there.
And this is the reason why polar representation is seldom used -- it's
virtually always a bad idea.
Generally speaking the best way of doing polar representation is to
put a wrapper over a cartesian complex type!

> I like it because it illustrates how library is more
> flexible than built-in...

More convincing I think will be when we have things like BigFloat
implemented, and can do complex!(BigFloat).


>
>
> Andrei
>
> On 03/25/2010 04:03 PM, Lars Tandle Kyllingstad wrote:
>>
>> Is anyone working, or planning to do work, on std.complex?  If not, and
>> if it is desirable, I could take a look at it. I guess the main thing
>> that is needed is to add overloaded operators. Is there anything else?
>>
>> Also, I wonder: How do you feel about renaming "modulus" and "angle" to
>> "mod" and "arg"? I seldom hear or use the term "angle" in relation to
>> complex numbers. "Argument" and "phase" are much more common, and the
>> standard mathematical notation for the argument of a complex number is
>> Arg(z). Also, "mod" and "arg" are nice and short, like "re" and "im".
>>
>> -Lars
>>
>>
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