MATLAB: Adding symbolic matrices along 3rd dimension

MATLABmatricessymbolicSymbolic Math Toolbox

Hi,
I have a symbolic 3-by-3-by-3 matrix as:
Q(:,:,1) = 
[ a, b, c]
[ d, e, f]
[ g, h, i]
Q(:,:,2) = 
[ a, d, g]
[ b, e, h]
[ c, f, i]
I added by sum command and I need to do it along 3rd dimension; so I did:
W = sum(Q,3)
But it returns me the error:
Error using mupadmex
Error in MuPAD command: Unable to define matrix over Dom::ExpressionField().
[(Dom::Matrix(Dom::ExpressionField()))::new]
Error in sym/privUnaryOp (line 1700)
            Csym = mupadmex(op,args{1}.s,varargin{:});
Error in sym/sum (line 502)
            s = privUnaryOp(A, 'symobj::prodsumdim', num2str(dim), '_plus');
I tried it with numeric matrices and it works. How Can I do it with symbolic matrices ?

Best Answer

clear Q
syms a b c d e f g h i 
Q(:,:,1) = [ a b  c;d e  f;g  h  i]
Q(:,:,2) = [ a, d, g;b, e, h; c, f, i]
[n1,n2,n3]=size(Q);
out=0;
for k=1:n3
  out=out+Q(:,:,k)
end
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