I believe I found a mistake in the undocumented PDL::Complex functions Catan2
and atan2.
pdl> use PDL::Complex
pdl> p atan2(1,0) # perl's function yields PI/2
1.5707963267949
pdl> p atan2(pdl(1),pdl(0)) # PDL's function also
1.5707963267949
pdl> p atan2(pdl(1)->r2C,pdl(0)->r2C) # but PDL::Complex's function disagrees
0 +0i
pdl> p atan2(pdl(0)->r2C, pdl(1)->r2C) # The first argument can't be zero.
NaN +NaNi
pdl> p atan2(pdl(0.000001)->r2C, pdl(1)->r2C) # But if ~0 result is not the
expected 0
1.5708 -5.55112e-17i
pdl>
I believe the error is in lines 905 and 906 of Basic/Complex/complex.pd
sub Catan2($$) { Catan Cdiv $_[1], $_[0] }
sub atan2($$) { Catan Cdiv $_[1], $_[0] }
where the 1's and 0's should be swapped.
sub Catan2($$) { Catan Cdiv $_[0], $_[1] }
sub atan2($$) { Catan Cdiv $_[0], $_[1] }
I guess it would be even better to use the complex log,
sub Catan2($$) { Clog( $_[1] + i*$_[0])/i }
as it wouldn't fail if the second argument is zero; it's real part
would coincide with the usual real atan2 of two real arguments.
Best regards,
Luis
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o
W. Luis Mochán, | tel:(52)(777)329-1734 /<(*)
Instituto de Ciencias Físicas, UNAM | fax:(52)(777)317-5388 `>/ /\
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