How to extract matrix with different starting index for each row?

I am not sure how to extract from a matrix a smaller matrix with different starting index for each row.

For example,

Original matrix (4x5):

[1 2 3 4 5]

[6 7 8 9 10]

[11 12 13 14 15]

[16 17 18 19 20]

Desired output (4,3):

[2 3 4]

[6 7 8]

[13 14 15]

[17 18 19]

where the starting index for each row is [2,1,3,2]

Thank you!

Answer 1

[Fangjun Jiang]

%%
Orig=transpose(reshape(1:20,5,[]))
StartPos=[2;1;3;2];
Wid=3;

row=repmat((1:size(Orig,1))',1,Wid);
col=StartPos+(0:Wid-1);
index=sub2ind(size(Orig),row,col);
out=Orig(index)

[Katherine Liu]

Thank you!!