Re: log for complex
On Wed, Mar 07, 2018 at 10:47:40AM +, J-S Caux via Digitalmars-d-learn
wrote:
> On Wednesday, 7 March 2018 at 10:28:23 UTC, Simen Kjærås wrote:
> > On Wednesday, 7 March 2018 at 10:10:49 UTC, J-S Caux wrote:
> > > On Wednesday, 7 March 2018 at 08:04:36 UTC, Simen Kjærås wrote:
> > > > auto log(T)(Complex!T x) {
> > > > import std.math : log;
> > > > return Complex!T(log(abs(x)), arg(x));
> > > > }
> > >
> > > Yes indeed I can do this, but isn't this inefficient as compared
> > > to what it should be? The internals of arg are presumable already
> > > doing part of/all the necessary work.
> >
> > arg is just atan2 in disguise, and doesn't do any logarithms. I
> > mean, in a way it does, but it's really just a fpatan instruction. I
> > don't expect there to be many optimization opportunities here.
[...]
> OK thanks Simen. Should your suggestion for repairing this omission be
> filed as a bugreport? I can of course implement it locally for myself,
> but the language should really provide this function directly.
Yes, please file a bug.
T
--
The trouble with TCP jokes is that it's like hearing the same joke over and
over.
Re: log for complex
On Wednesday, 7 March 2018 at 10:28:23 UTC, Simen Kjærås wrote:
On Wednesday, 7 March 2018 at 10:10:49 UTC, J-S Caux wrote:
On Wednesday, 7 March 2018 at 08:04:36 UTC, Simen Kjærås wrote:
auto log(T)(Complex!T x) {
import std.math : log;
return Complex!T(log(abs(x)), arg(x));
}
Yes indeed I can do this, but isn't this inefficient as
compared to what it should be? The internals of arg are
presumable already doing part of/all the necessary work.
arg is just atan2 in disguise, and doesn't do any logarithms. I
mean, in a way it does, but it's really just a fpatan
instruction. I don't expect there to be many optimization
opportunities here.
--
Simen
OK thanks Simen. Should your suggestion for repairing this
omission be filed as a bugreport? I can of course implement it
locally for myself, but the language should really provide this
function directly.
Re: log for complex
On Wednesday, 7 March 2018 at 10:10:49 UTC, J-S Caux wrote:
On Wednesday, 7 March 2018 at 08:04:36 UTC, Simen Kjærås wrote:
auto log(T)(Complex!T x) {
import std.math : log;
return Complex!T(log(abs(x)), arg(x));
}
Yes indeed I can do this, but isn't this inefficient as
compared to what it should be? The internals of arg are
presumable already doing part of/all the necessary work.
arg is just atan2 in disguise, and doesn't do any logarithms. I
mean, in a way it does, but it's really just a fpatan
instruction. I don't expect there to be many optimization
opportunities here.
--
Simen
Re: log for complex
On Wednesday, 7 March 2018 at 08:04:36 UTC, Simen Kjærås wrote:
On Wednesday, 7 March 2018 at 07:42:37 UTC, J-S Caux wrote:
Simple question: how do I get the log of a complex number?
If I try the simple
logtest = log(complex(1.0, 2.0))
I get the compiler error
Error: function core.stdc.math.log(double x) is not callable
using argument types (Complex!double)
Some basic functions are described in
https://dlang.org/phobos/std_complex.html, but not the log...
That seems like an oversight. For now, this should work:
auto log(T)(Complex!T x) {
import std.math : log;
return Complex!T(log (abs(x)), arg(x));
}
--
Simen
Yes indeed I can do this, but isn't this inefficient as compared
to what it should be? The internals of arg are presumable already
doing part of/all the necessary work.
Re: log for complex
On Wednesday, 7 March 2018 at 07:42:37 UTC, J-S Caux wrote:
Simple question: how do I get the log of a complex number?
If I try the simple
logtest = log(complex(1.0, 2.0))
I get the compiler error
Error: function core.stdc.math.log(double x) is not callable
using argument types (Complex!double)
Some basic functions are described in
https://dlang.org/phobos/std_complex.html, but not the log...
That seems like an oversight. For now, this should work:
auto log(T)(Complex!T x) {
import std.math : log;
return Complex!T(log (abs(x)), arg(x));
}
--
Simen
log for complex
Simple question: how do I get the log of a complex number? If I try the simple logtest = log(complex(1.0, 2.0)) I get the compiler error Error: function core.stdc.math.log(double x) is not callable using argument types (Complex!double) Some basic functions are described in https://dlang.org/phobos/std_complex.html, but not the log...
