Thread Subject: Noob: How to use a variable as parameter in SS-model???

Hi!
I'm quite experienced with MatLab but not with Simulink...
So this is probably very simple for you guys:

I have a state-space-block in Simulink which requires to define the matrices A,B,C,D.
Normally you define these matrices directly in the Function Block Properties with numeric values. But I would like to define these matrices with values, called a and b, which I have calculated with another block.
The ss-block only has one input and one output for the x and u vector. So I can't get my a and b into the ss-block by connecting it with lines....

When I try to run the model Simulink complains, that a and b are unknown variables...

Thanks!

Hello,
Are you using the sim command? If so, have you checked the default source and destination workspaces (see the simset documentation).
Mathieu

"Volker Klink" <volker.v.klinkNOSPAM@daimler.com> wrote in message <gh0qsh$alp$1@fred.mathworks.com>...
> Hi!
> I'm quite experienced with MatLab but not with Simulink...
> So this is probably very simple for you guys:
>
> I have a state-space-block in Simulink which requires to define the matrices A,B,C,D.
> Normally you define these matrices directly in the Function Block Properties with numeric values. But I would like to define these matrices with values, called a and b, which I have calculated with another block.
> The ss-block only has one input and one output for the x and u vector. So I can't get my a and b into the ss-block by connecting it with lines....
>
> When I try to run the model Simulink complains, that a and b are unknown variables...
>
> Thanks!

> Are you using the sim command? If so, have you checked the default source and destination workspaces (see the simset documentation).

Well, I tried not to use a MatLab script at all....
But I guess I have to check that out...

Hello,
Then, I don't see the problem. If you have for instance a gain which is set for instance to "a+b", and that a and b have not been defined in mask or model workspaces, then Simulink looks for a and b in the base workspace (if you launched your simulation using the "play" button) to evaluate the expression. So you just need to define a and b in the base workspace. Have you built the model yourself? Does the model have any callbacks that clear the workspace?
Mathieu


"Volker Klink" <volker.v.klinkNOSPAM@daimler.com> wrote in message <gh10cq$br6$1@fred.mathworks.com>...
> > Are you using the sim command? If so, have you checked the default source and destination workspaces (see the simset documentation).
>
> Well, I tried not to use a MatLab script at all....
> But I guess I have to check that out...

"Volker Klink" <volker.v.klinkNOSPAM@daimler.com> wrote in message <gh0qsh$alp$1@fred.mathworks.com>...
> Hi!
> I'm quite experienced with MatLab but not with Simulink...
> So this is probably very simple for you guys:
>
> I have a state-space-block in Simulink which requires to define the matrices A,B,C,D.
> Normally you define these matrices directly in the Function Block Properties with numeric values. But I would like to define these matrices with values, called a and b, which I have calculated with another block.
> The ss-block only has one input and one output for the x and u vector. So I can't get my a and b into the ss-block by connecting it with lines....
>
> When I try to run the model Simulink complains, that a and b are unknown variables...
>
> Thanks!

If you have your A, B, C and D calculated on signal lines, you should just build the equations with base blocks. Integrator, matrix multiply, sum. The state space block uses constant values for A, B, C and D. It sounds like your values are not constant so the State Space block is not right for your system.

Seth Popinchalk

Check out my Simulink blog: http://blogs.mathworks.com/seth/
Senior Applications Engineer
The MathWorks, Inc.