# How to correct "Undefined function 'mtimes' for input arguments of type 'cell'."

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Richard Westgarth on 21 Nov 2022
Commented: Richard Westgarth on 21 Nov 2022
I am trying to estimate parameters of some ODEs that describe the velocity vector of a wheeled mobile robot using the system identification toolbox. Specifically, I am trying to solve a non linear grey box model to find these parameters.
When I run the model I get the following error:
Error using iddata/nlgreyest
Error or mismatch in the specified ODE file "threewheeledomni_modelFile."
The error message is: "Undefined function 'mtimes' for input arguments of type 'cell'."
Here is the code for the ODE, the other file is too much to copy in here:
function[dx,y] = threewheelomni_modelFile(t,x,u,alpha1,alpha2,alpha3,beta1,beta2,beta3,gamma1,gamma2,gamma3,l,r,varargin)
alpha=[alpha1,alpha2,alpha3];
beta =[beta1,beta2,beta3];
gamma=[gamma1,gamma2,gamma3];
y=x;
rotMat = [cos(x(3)),-sin(x(3)),0;sin(x(3)),cos(theta0),0;0,0,1];
J1 = [sin(alpha(1)+beta(1)+gamma(1)),-cos(alpha(1)+beta(1)+gamma(1)),-l*cos(beta(1)+gamma(1));...
sin(alpha(2)+beta(2)+gamma(2)),-cos(alpha(2)+beta(2)+gamma(2)),-l*cos(beta(2)+gamma(2));...
sin(alpha(3)+beta(3)+gamma(3)),-cos(alpha(3)+beta(3)+gamma(3)),-l*cos(beta(3)+gamma(3))];
J2 = [r*cos(gamma1),0,0;0,r*cos(gamma2),0;0,0,r*cos(gamma3)];
dx = inv(rotMat)*inv(J1)*J2*u;
##### 2 CommentsShowHide 1 older comment
Richard Westgarth on 21 Nov 2022
Correct. Im saying that was a mistake on my part. theta0 shouldnt have been a fixed parameter, its a variable. I updated the code such that theta0 is calculated from an integral function of x(3) now I'm rolling along ok. Its also possible I attached mismatched files. Thanks for the response, you helped me solve this one by highlighting that detail.

Walter Roberson on 21 Nov 2022
The mlx constructs 11 parameters starting from alpha1 . However the modelFile expects 12 parameters starting from theta0
Richard Westgarth on 21 Nov 2022
theta0 should have been the 3rd element of the state vector. Silly question, sorry about that.

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