I’m currently working on making creal and cimag return real data rather than
complex, which I’m doing by implementing a “real” type qualifier (in PP
terminology), so:
Pars => “a(); real [o] b()”
This is also necessary to implement irfftn() in PDL::FFTW3 with native complex
data, because the library itself takes complex data and returns real, and
currently PDL makes all data parameters be the same unless a type-qualifier is
given, and I didn’t want to have to make separate cfloat and cdouble versions.
I think that comparisons (including sorting) of complex data other than an
equality test (and approx) should simply throw an exception, as they aren’t
mathematically valid at all. I also think that the equivalent should be done in
PDL::Complex, despite it not currently being an error. What do others think?
In a similar vein: is it really useful to call creal/cimag on real data? It
seems to me that too should throw an exception.
Best regards,
Ed
From: Luis Mochan<mailto:moc...@icf.unam.mx>
Sent: 26 March 2021 05:30
To: pdl-devel@lists.sourceforge.net<mailto:pdl-devel@lists.sourceforge.net>
Subject: Re: [Pdl-devel] [Pdl-general] PDL 2.029 released
I started playing with the new complex numbers. I find it nice
and useful that creal and cimag can be applied to real pdl's, but the
results are promoted to complex:
pdl> $x=pdl(1)
pdl> p $x
1
pdl> p $x->creal
1+0i
pdl> p $x->cimag
0+0i
Equality and inequality comparisons do work but they also return
complex values:
pdl> p $x==1
1
pdl> p $x->creal==1
1+0i
pdl> p $x->creal==2
0+0i
pdl> p $x->creal!=2
1+0i
This is troublesome, as their boolean interpretation is not correct:
pdl> print +($x->creal==1)?'yes':'no'
yes
pdl> print +($x->creal==2)?'yes':'no'
yes
pdl> print +($x==2)?'yes':'no'
no
On the other hand, greater than, lower than, etc. do compare the real
parts only and return a real value.
pdl> $y=ci
pdl> p $y<1
1
pdl> p $y<ci
0
pdl> p $y<=0.01*ci
1
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