MATLAB: Error using sqpInterface Objective function is undefined at initial point.

double inverted pendulumfminconinverted pendulum

while using nmpc example of the inverted pendulum.I am getting this error. I just change model to double pendulum model in pendulumCT.m file. what should I do?

Error using sqpInterface
Objective function is undefined at initial point. Fmincon cannot continue.
Error in fmincon (line 808)
    [X,FVAL,EXITFLAG,OUTPUT,LAMBDA,GRAD,HESSIAN] = sqpInterface(funfcn,X,full(A),full(B),full(Aeq),full(Beq), ...
Error in nmpc (line 52)
    uopt = fmincon(COSTFUN,uopt,[],[],[],[],LB,UB,CONSFUN,options);

Best Answer

First try evaluating your cost function with your initial guess and see if you can actually get an output. I believe that fmincon expects the output of the cost function to be a real scalar value. Double check that you're not outputting a complex quantity.

Related Solutions

MATLAB: Hi all; I try to use fmincon in order to find the optimal control force F for an active suspension system, every time I run fmincon, F and the objective function did not change. Kindly, can any on explain to me why I get this problem. Thanks

Did you try plotting your objective function to make sure that it is not constant near the initial point? Are you sure that you calculated the gradient of your function correctly? If so, then tell fmincon that you are supplying the gradient by setting

options.GradObj = 'on';

If you are not supplying a gradient, then you might need larger finite difference steps sizes, as described in the documentation on optimizing simulations.

Good luck,

Alan Weiss

MATLAB mathematical toolbox documentation

MATLAB: How can calcuate the lines of code efficiently

Yes, you can if you avoid using a loop and vectorize your code - see here:

tic
%%%code

nx=512;
ny=nx;
dx=1;
dy=dx;
format long;
nxny=nx*ny;
r=zeros(1,nx);
r(1:2)=[2,-1];
T=toeplitz(r);
E=speye(nx);
grad=-(kron(T,E)+kron(E,T));%Tensor


%-- for periodic boundaries


ii=(0:nx-1).*nx+1;
jj = ii+nx-1;
grad(ii,jj)=1.0;
grad(jj,ii)=1.0;
kk=(nxny-nx+1):nxny;
grad(1:nx,kk)=1.0;
grad(kk,1:nx)=1.0;
grad = grad /(dx*dy);
toc
Elapsed time is 0.145899 seconds.

Your code:

tic
%%%code
nx=512;
ny=nx;
dx=1;
dy=dx;
format long;
nxny=nx*ny;
r=zeros(1,nx);
r(1:2)=[2,-1];
T=toeplitz(r);
E=speye(nx);
grad=-(kron(T,E)+kron(E,T));%Tensor
%-- for periodic boundaries
for i=1:nx
    ii=(0:nx-1).*nx+1;
    jj=ii+nx-1;
    grad(ii,jj)=1.0;
    grad(jj,ii)=1.0;
    kk=nxny-nx+i;
    grad(i,kk)=1.0;
    grad(kk,i)=1.0;
end 
toc
Elapsed time is 11.333450 seconds.

Are the results correct? - to check this we call one of the results grad1 and subtract grad1 from grad:

nx=512;
ny=nx;
dx=1;
dy=dx;
format long;
nxny=nx*ny;
r=zeros(1,nx);
r(1:2)=[2,-1];
T=toeplitz(r);
E=speye(nx);
grad=-(kron(T,E)+kron(E,T));%Tensor
%-- for periodic boundaries
for i=1:nx
    ii=(0:nx-1).*nx+1;
    jj=ii+nx-1;
    grad(ii,jj)=1.0;
    grad(jj,ii)=1.0;
    kk=nxny-nx+i;
    grad(i,kk)=1.0;
    grad(kk,i)=1.0;
end 
ii=(0:nx-1).*nx+1;
jj = ii+nx-1;
grad(ii,jj)=1.0;
grad(jj,ii)=1.0;
kk=(nxny-nx+1):nxny;
grad(1:nx,kk)=1.0;
grad(kk,1:nx)=1.0;
grad1 = grad /(dx*dy);
expect_all_zeros = grad1-grad
expect_all_zeros =
   All zero sparse: 262144×262144

Appears to work fine...

Best Answer

Related Solutions

MATLAB: Hi all; I try to use fmincon in order to find the optimal control force F for an active suspension system, every time I run fmincon, F and the objective function did not change. Kindly, can any on explain to me why I get this problem. Thanks

MATLAB: How can calcuate the lines of code efficiently

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