Hello been trying to extract array from a big matrix so because of that taken magic(5) but issue is that when using for loop it works but trying to use in vectorization it gives error

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ARSALAN RIAZ 2017-7-12

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评论： Walter Roberson 2017-7-15

a=magic(5);
c=zeros(3,3,3);
for i=1:3
c(:,:,i)=a(i:3+(i-1),1:3)
end

above code works.

but issue is when using

i=1:3;
c(:,:,i)=a(i:3+(i-1),1:3)

it gives error

Assignment has fewer non-singleton rhs dimensions than non-singleton 
subscripts

a(i:3+(i-1),1:3) is use to extract 3 x 3 matrix

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回答（1 个）

Walter Roberson 2017-7-12

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在 MATLAB Online 中打开

When you do

i=1:3;
a(i:3+(i-1),1:3)

then you are attempting to use a vector in the base position and a vector in the final position for the colon operator. Look again at https://www.mathworks.com/help/matlab/ref/colon.html#bviscw3-1 and see that those are required to be scalars.

MATLAB does not provide any direct way to do the kind of ragged indexing you want to do.

The approach you need to take in MATLAB is to use sub2ind() or equivalent to construct the linear indexes of the elements you wish to extract, and use linear indexing of the source array.