ForwardDynamics - Specifying dt steps error

[Pavlos Silvestros]

Hello all,

I am running forward dynamics simulations and trying to extract values for the states at specific time intervals. It was suggested to assign an initial states file with the wanted time step interval. I have assigned a file with 10 time steps and also all the frames of interest but I am getting th following error:

ForwardTool::run() caught exception
IntegRKF.integrate: ERR- specified dt stepping notpossible-- time array does not cover the requested integration interval.

I have checked that my initial time corresponds to one of the time stamps but can't figure it the problem.

Any help would be greatly apprecieted!

Thank you in advance.

Best regards,
Pavlos

[Christopher Dembia]

Could you attach your setup file? Could you simply interpolate the output afterwards to obtain values at the desired times? Have you tried using different time intervals?

Forward dynamics only takes the first state in a states file for the initial state, and will ignore all subsequent states provided.

[Pavlos Silvestros]

Hi Chris

Thank you for your reply. I have attached the settings file and the initial states files I have used. I have used different time steps but no luck. I have thought of interpolating but I thought they may be problems because of the varying time step of the output file. I am using force data at a frequency of 1 MHz and simulating for 0.007805 s.

I am running the FD tool through the Matlab API.

Thanks for your help again

Best regards
Pavlos

[Thomas Uchida]

Please read the comment in FD_Setup.xml for the use_specified_dt property:
<!--Flag (true or false) indicating whether or not the integrator should use a particular time stepping. If true, the time stepping is extracted from the initial states file. In this situation, therefore, the initial states file must contain all the time steps in a simulation and be written out to high precision (usually 20 decimal places). Setting this flag to true can be useful when reproducing a previous forward simulation with as little drift as possible. If this flag is false, the integrator is left to determine its own time stepping.-->

You have indicated an initial_time of 0 and a final_time of 0.007805, but the time column in your .sto file begins at 0.000333333 and ends at 0.007666667. It looks like you either need to change the initial_time and final_time to 0.000333333 and 0.007666667, respectively, or adjust the time column in your .sto file to cover the range over which you are simulating.

[Pavlos Silvestros]

Good Morning Tom,

Thanks for your help!

I tried it in the GUI now and it worked. Yesterday I was trying as you suggested with the time window/column in the API but I must of been doing something else wrong.

I will get back to you when I try it again in the API.

Thank you very much again!

Best regards,
Pavlos