Bug? on transferring from simple vector to state

[barak ostraich]

I'm using a vector of 1 to 10 to check how it transfers to state

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st=model.initSystem(); %empty state
vs=org.opensim.modeling.Vector; % empty vector
v=[1:st.getNQ]; % matlab vector of 1 to 10
st.setQ(vs.createFromMat(v)); %passing the 1:10 vector to state Q
so=model.getStateVariableValues(st).getAsMat;

I get:
1 0 2 0 3 0 4 0 7 0 9 0 5 0 8 0 10 0 6
The zeros are the U, but why the numbers are mixed??

[Ayman Habib]

Hello,

I don't believe the OpenSim API makes any claims about the ordering of the Qs in the state vector, as such I don't believe this is a bug. There're model methods to obtain coordinates in multibody tree order e.g.

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getCoordinatesInMultibodyTreeOrder

that you may find useful, however.

Hope this helps,
-Ayman

[barak ostraich]

thanks
i understand the meaning. But how can i get members of the vector i got in Matlab
i get "org.opensim.modeling.SWIGTYPE_p_std__vectorT_SimTK__ReferencePtrT_OpenSim__Coordinate"

how can i get the members of the vector in Matlab?

[Thomas Uchida]

But how can i get members of the vector i got in Matlab

You can find some examples here:
- The "Scripting" section of the User's Guide: https://simtk-confluence.stanford.edu/d ... /Scripting
- Your "Resources" directory (e.g., C:\OpenSim 4.1\Resources\Code\Matlab)
- On GitHub: https://github.com/opensim-org/opensim- ... b/examples
It isn't clear what you are trying to do with "org.opensim.modeling.SWIGTYPE_p_std__vectorT_SimTK__ReferencePtrT_OpenSim__Coordinate", but you can try the "get()" method.

[barak ostraich]

i cant get any value from "getCoordinatesInMultibodyTreeOrder"
the get() is not working

i see that similar question was asked on 2017
https://github.com/opensim-org/opensim-core/issues/1858

[Thomas Uchida]

What is it you are trying to do? If you need the value of a coordinate, you can do something like the following:

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joint = model.getJointSet().get('myJoint')
pin = osim.PinJoint.safeDownCast(joint)
angle = pin.getCoordinate().getValue(state)

The recommended strategy for interacting with the model is to use the OpenSim modelling interface.

[barak ostraich]

Im sorry for the misunderstanding.
I need to use the state.setY(someVector).
But when i use it, I get it in wrong order in

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model.getStateVariableValues(state)

How will i know in advance what is the order of setY?

thanks

[Thomas Uchida]

How will i know in advance what is the order of setY?

I think the ordering of states in the state vector will emerge from a depth-first traversal of the Component ownership tree. (The ordering will be the same each time you run your code, but the API doesn't guarantee this.) You could use the following algorithm to determine where each coordinate ends up in the state:

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for i from 1 to the number of coordinates in the model :
    set all states to zero
    set the ith model coordinate to 0.1
    find the index of the only nonzero entry in the state vector
    store the index in a lookup table that relates each coordinate to the corresponding index in the state vector
end for