Insert Matrix into Matrix and don't care if some of the numbers fall off the edge

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Andrew Luce
Andrew Luce 2021-8-12
回答： the cyclist 2021-8-12
I'm trying to make a little game. I have a 2 part question. How can I insert a matrix in a matrix where I do not care if the some of the inserted matrix falls outside the matrix I am inserting it into. Except, I don't want the center of the inserted matrix to be lost,
Thank you
Andrew
example
A= 1 1 1
1 2 1
1 1 1
B= 0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
B into A at (4,5) (coordinates based on center of A)
Result = 0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 1 1 1
0 0 0 1 2 1
  1 个评论
Walter Roberson
Walter Roberson 2021-8-12
What should happen in the case where the center of the inserted matrix would get lost?
I do not see you inserting B into A; I see you inserting A into B ?

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回答（1 个）

the cyclist
the cyclist 2021-8-12
Ran in:
Probably not the most efficient, but I believe this does what you want:
% Arrays
A= [1 1 1
1 2 1
1 1 1];
B= [0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
0 0 0 0 0 0
];
% Where to center
ci = 4;
cj = 5;
% Get sizes
[mA, nA] = size(A);
[mB, nB] = size(B);
% Calculate necessary "padding" around B, which will be trimmed later
pad = (mA-1)/2;
% Initialize output as padded size
output = nan(mB+2*pad,nB+2*pad);
% Insert B into padded array
output(pad+1:end-pad,pad+1:end-pad) = B;
% Insert A into padded array, at specified coordinates
output(ci:ci+mA-1,cj:cj+nA-1) = A;
% Remove the padding (and extraneous elements of A)
output = output(pad+1:end-pad,pad+1:end-pad)
output = 4×6
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 1 2 1

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