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Re: matrix exponential used by the control package

From: Doug Stewart
Subject: Re: matrix exponential used by the control package
Date: Mon, 20 Jul 2020 17:22:20 -0400

On Mon, Jul 20, 2020 at 4:38 PM Torsten Lilge1960 Blue Heron Drive, <ttl-octave@mailbox.org> wrote:
Hi everyone,

the control package uses the SLICOT function mb05nd [1]
(__sl_mb05nd__()) instead of the octave function expm() for the matrix
exponential. The problem with mb05nd is that when discretizing a static
gain in state space results in

>> [a,b,c,d] = ssdata (c2d (ss (tf (1,1)),1))
a = [](1x0)
b = 0
c = [](1x0)
d = 1

Instead, using expm() leads to the correct result

>> [a,b,c,d] = ssdata (c2d (ss (tf (1,1)),1))
a = [](0x0)
b = [](0x1)
c =
d = 1

Are there any reasons against using expm()?


[1] http://slicot.org/objects/software/shared/doc/MB05ND.html

Is there a difference in speed?
If it is slower then we should look and see where the '0" is coming from.

DASCertificate for 206392

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