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Substitute syms in 2D array to have 3D array

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Saurav Agarwal
Saurav Agarwal 2012-12-22
I have a 2D array of syms and I want to substitute the syms variables with 1D array. How do i do it? If a form a loop it takes a long runtime.
sample code:
syms a b c
arr=[0 0 0;0 0 0;a b c];
a=[1 2 3 4 5]';
b=[2 3 4 5 6]';
c=[5 6 7 8 9]';
subs(arr)
The output should be a 3x3x5 matrix. Please help
I have the following code using loops:
syms a b c
arr=[0 0 0;0 0 0;a b c];
J=zeros(3,3,5);
a1=[1 2 3 4 5]';
b1=[2 3 4 5 6]';
c1=[5 6 7 8 9]';
for i=1:5
a=a1(i);
b=b1(i);
c=c1(i);
J(i)=subs(arr);
end

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采纳的回答

Walter Roberson
Walter Roberson 2012-12-22
subs() is not able to do this for you, as you need to replicate the other elements of the array. I do not think you will be able to do this without a loop (though you can probably hide the loop using arrayfun())
  1 个评论
Walter Roberson
Walter Roberson 2012-12-23
You initialize J as numeric zeros of size (3,3,5), but you assign to J(i) which would be J(i,1,1) a single numeric location.
Try
syms a b c
arr=[0 0 0;0 0 0;a b c];
a1=[1 2 3 4 5]';
b1=[2 3 4 5 6]';
c1=[5 6 7 8 9]';
J = double( arrayfun(@(aval, bval, cval) subs(arr, {a, b, c}, {aval, bval, cval}), a1, b1, c1) );
You might have to use
J = double( cell2mat( arrayfun(@(aval, bval, cval) subs(arr, {a, b, c}, {aval, bval, cval}), a1, b1, c1, 'Uniform', 0) ));

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更多回答（1 个）

Saurav Agarwal
Saurav Agarwal 2012-12-23
Taking a loop take a lot of time.. is there an alternate way? please help.
  2 个评论
Walter Roberson
Walter Roberson 2012-12-23
I cannot think of any way of doing this that does not involve a loop.
If you show the loop that you have coded, we can examine it and see if we can suggest improvements.
Saurav Agarwal
Saurav Agarwal 2012-12-23
I have edited the question to show the code using loop.

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