[SciPy-Dev] Sylvester equation solver for complex matrices

Warren Weckesser warren.weckesser@enthought....
Sat Feb 11 11:24:51 CST 2012


On Sat, Feb 11, 2012 at 4:45 AM, Nils Wagner
<nwagner@iam.uni-stuttgart.de>wrote:

> Hi all,
>
> I run a short test on the recent solver for Sylvester
> equations.
> In case of complex input matrices the method returns
>  ** On entry to ZTRSYL parameter number  2 had an illegal
> value
>
> Nils
>
>

Thanks, Nils.  The new solve_sylvester function didn't handle complex
matrices correctly. I have submitted a pull request (
https://github.com/scipy/scipy/pull/155) that should fix this.

Warren



> import numpy as np
> from scipy import linalg as la
> np.random.seed(10)
> a = np.random.rand(20,20)+1j*np.random.rand(20,20)
> b = np.random.rand(20,20)+1j*np.random.rand(20,20)
> q = np.random.rand(20,20)+1j*np.random.rand(20,20)
>
> x = la.solve_sylvester(a,b,q)
> res = la.norm(np.dot(a,x)+np.dot(x,b)-q)
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