Put a small matrix in a bigger one.

I want to put a small matrix (p*q) called B into a bigger matrix (m*n) called A. How can I do it. Matrix B should be put on the left-right corner of matrix A.

for better understanding take a look on this image:

Answer 1

[chibole]

function A = MatrixReplace(A,B)
    [p,q] = size(B); 
    A(end-p+1:end, end-q+1:end) = B; 
end

[Marta Pinto]

Thank you! I had a similar problem and based on your answer and this question i could do it.

[Image Analyst]

Be careful with this code. For one thing, it puts the pasted matrix in the lower right corner, not at some arbitrary row and column (row "i" and column "j") like the poster asked for. It also has no error checking, has no comments, and doesn't use descriptive variable names. Personally, I would not use this code in my company. For more flexible and robust way, see my answer.

[chibole]

"For one thing, it puts the pasted matrix in the lower right corner" That is what is asked in the question.

Answer 2

[Image Analyst]

Try this fairly robust, more general code where you can specify the upper left corner and it will check to make sure the small array does not go outside the big array.:

% Create sample data:
big = ones(10)
small = 9 * ones(3)

% Get sizes
[rowsBig, columnsBig] = size(big);
[rowsSmall, columnsSmall] = size(small);
% Specify upper left row, column of where
% we'd like to paste the small matrix.
row1 = 5;
column1 = 3;
% Determine lower right location.
row2 = row1 + rowsSmall - 1
column2 = column1 + columnsSmall - 1
% See if it will fit.
if row2 <= rowsBig
  % It will fit, so paste it.
  big(row1:row2, column1:column2) = small
else
  % It won't fit
  warningMessage = sprintf('That will not fit.\nThe lower right coordinate would be at row %d, column %d.',...
    row2, column2);
  uiwait(warndlg(warningMessage));
end

[Preet Lal]

Hello @Image Analyst

Thank You for sharing code publicly.

I have one doubt....

I am working on multiple matrices, and some of the row/column are common to each matrices like in 5X5 matrices, 2X3 is overlapping each other. How I can calculate mean for that specific overlapping row and cols and fill into bigger matrix.

[Image Analyst]

If you know the size of the matrices to be pasted onto the underlying matrix, and the locations, then you can figure out the overlap region. Then just use normal indexing to get the mean. For example if you're pasting a 2x3 into the upper left corner of a 5x5 matrix, and a 2x3 onto the upper right corner, then the last column of the first matrix you paste will overlap the left column of the second 2x3 matrix, and they are both in column 3 of the 5x5 matrix.

[Preet Lal]

Thanks @Image Analyst

I am not clear,

If possible could you please share a short demo code.

Answer 3

[Andrei Bobrov]

Use function padarray from Image Processing Toolbox

A(padarray(true(size(B)),size(A)-size(B),'pre')) = B;

or

A(blkdiag(false(size(A)-size(B)),true(size(B)))) = B;