Use Matrix element as function input

Question

Fred John 2014-12-30

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https://ww2.mathworks.cn/matlabcentral/answers/168532-use-matrix-element-as-function-input

评论： Fred John 2014-12-30

采纳的回答： Geoff Hayes

在 MATLAB Online 中打开

Hi!

I have a 10x2 Matrix A, defined as A=R*T. Where R and T are also Matrices.

I have:

function [S] = myFunction(q,w)
S=[q 0 w 0 0;
 w 0 0 q 0;
 q w 0 0 0;
 w 0 0 q 0;
 0 0 0 w q];
q=A(1,1);
w=A(1,2);

The aim is for the function to take the (1,1) & (1,2) elements of the Matrix A and place them in the Matrix S. But I'm getting the error:

Undefined function or method 'A' for input arguments of type 'double'

Any help would be great. Thanks!

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Answer 1

Geoff Hayes 2014-12-30

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Fred - I think the order of your operations is incorrect. If all of your above code (less the function signature) is in the body of the function, then the error messages makes sense since you are trying to reference the matrix A without it being passed into the function. I think that you want to do the following instead

 function [S] = myFunction(A)
 % now determine q and w
 q=A(1,1);
 w=A(1,2);
 % initialize S
 S=[q 0 w 0 0;
 w 0 0 q 0;
 q w 0 0 0;
 w 0 0 q 0;
 0 0 0 w q];

In the Command Window (or in your script), you would initialize A and then pass it as a parameter to your function, myFunction which would extract the values for q and w. Try the above and see what happens!