Assigning a submatrix to an existing matrix

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(12-19-2023 10:17 AM)deSitter Wrote:  How do I say put a 2x2 matrix into an existing 4x4 matrix? Say I want to overwrite the elements in rows 1,2 and columns 3,4 with a 2x2 matrix - can I do this by direct assignment? Thanks in advance.

4x4 matrix:
mt1:=[[1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16]]

2x2 matrix:
mt2:=[[−1,−2],[−3,−4]]

REPLACE(mt1,{1,3},mt2)

and you will get:

Code:

[[ 1, 2,−1,−2],
 [ 5, 6,−3,−4],
 [ 9,10,11,12],
 [13,14,15,16]]

Piotr