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

Question

Andrew Luce 2021-8-12

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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
2 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 

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

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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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Answer 1

the cyclist 2021-8-12

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在 MATLAB Online 中打开

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