WARNING: Millard2012AccelerationMuscle

[Sandy Tschounes]

Hi OSIM-Team

During running a Static Optimization the following warnings show up:

time = 7.42 Performance =367.867 Constraint violation = 2.7079e-005
WARNING: No suitable initial conditions found for
tfl_l:
by

WARNING: Millard2012AccelerationMuscle::computeInitialFiberEquilibrium(SimTK::State& s)
Continuing with an initial fiber force, length and velocity of 0, 0.177001 and 0
Here is a report from the routine:

Solution Error : 1.148576 > tol (0.000006)
Newton Iterations : 500 of max. iterations (500)
Check that the initial activation is valid, and that the whole
length doesn't produce a pennation angle of 90 degrees, nor a fiber
length less than 0:
Activation : 0.000000
Whole muscle length : 1.#QNAN0

I don't understand what exactly this means?

Best, Sandy

[jimmy d]

From the source code, it looks like the muscle(s) cannot find a solution after the maximum amount of optimizer iterations (500). The message then outlines some things to check to help it get working.

Is there any particular reason why you are using this Muscle model (Millard Acceleration)? We tend to recommend people use the Millard Equilibrium muscle since it can be more stable.