MATLAB: How to get a matrix as a input & output with using fsolve

fsolveMATLABnonlinear

Hi everyone. I am trying to solve a group of nonlinear equations. It supposes to return a matrix, but the error keeps appearing.
Any advice or suggestion is appreciated.
Index in position 3 exceeds array bounds (must not exceed 1).
Error in Untitled8>myfun (line 20)
        F=[1/ds*(y(:,:,3)+M11)*(y(:,:,1)-y11)...
Error in fsolve (line 242)
            fuser = feval(funfcn{3},x,varargin{:});
Error in Untitled8 (line 5)
[x,fval]=fsolve(@myfun,x0);
Caused by:
    Failure in initial objective function evaluation. FSOLVE cannot
    continue.
    clear all
  clc
  a=randi(6,6)
  x0=[a;a;a;a;a;a;a;a];
  [x,fval]=fsolve(@myfun,x0);
   function F = myfun(y)
   ds=1;dt=1;
      M11=randi(6,6);
      N11=randi(6,6);
      Q11=randi(6,6);
      y11=randi(6,6);
      M21=randi(6,6);
      N21=randi(6,6);
      Q21=randi(6,6);
      y21=randi(6,6);
          F=[1/ds*(y(:,:,3)+M11)*(y(:,:,1)-y11)...
              +1/ds*(y(:,:,4)+M21)*(y(:,:,2)-y21)...
              -1/dt*(N21+N11)*(y21-y11)...
              -1/dt*(y(:,:,5)+y(:,:,6))*(y(:,:,2)-y(:,:,1))...
              -Q11-y(:,:,7)-Q21-y(:,:,8);];
   end

Best Answer

x0 = cat(3, a,a,a,a,a,a,a,a)
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