[SciPy-dev] sinm and cosm for matrices with real coefficients

Robert Kern robert.kern at gmail.com
Sun Apr 30 00:08:29 CDT 2006


Vanuxem Grégory wrote:
> Hi,
> 
> The code of cosm and sinm for matrices with real coefficients can be
> improved.
> 
> The actual code is something like:
> 
> sinm :  (expm(j * M) - expm(- j*M)) / (2 * j)
> 
> cosm :   (expm(j * M) + expm(- j* M)) / 2
> 
> But this can be changed to (only for matrices with real coefficients):
> 
> sinm : imaginary_part(expm(j * M))
> 
> cosm : real_part(expm(j * M))

However, we want the functions to work on complex matrices, too. The
optimization is probably not worth the extra code to dispatch on the datatype.
Of course, if someone comes along with a use-case where they need the extra
speed, and they have a patch, unit tests, and benchmarks ready, we'd probably
put it in.

Thank you for your interest, though. Please let us know if you find anything
else that seems bogus.

-- 
Robert Kern
robert.kern at gmail.com

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco




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