# matrix exponential used by the control package

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## matrix exponential used by the control package

 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 = [](1x0) d = 1 Are there any reasons against using expm()? Torsten [1] http://slicot.org/objects/software/shared/doc/MB05ND.html
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## Re: matrix exponential used by the control package

 On Mon, Jul 20, 2020 at 4:38 PM Torsten Lilge1960 Blue Heron Drive, <[hidden email]> 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 = [](1x0) d = 1 Are there any reasons against using expm()? Torsten [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.-- DAS
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## Re: matrix exponential used by the control package

 On Mon, 2020-07-20 at 17:22 -0400, Doug Stewart wrote: > > > On Mon, Jul 20, 2020 at 4:38 PM Torsten Lilge1960 Blue Heron Drive, < > [hidden email]> 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 = > > [](1x0) > > d = 1 > > > > Are there any reasons against using expm()? > > > > Torsten > > > > > > [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. __sl_mb05nd__ is a compiled function and - at least on my system - approx. 20 times faster. Torsten