# How to replace the entries of a matrix by another matrix?

I have a two matrix mm and nn. Matrix mm is of dimension 8 cross 8 and nn is of dimensions 4 cross 4. I want to replace the first four rows and columns in mm by nn. How to do this?

mm = ConstantArray[q, {8, 8}]
nn = ConstantArray[r, {4, 4}]

• Try mm[[;; 4, ;; 4]] = nn. Apr 4, 2019 at 7:07

you can use Table and make any changes you like
Table[mm[[j, k]] = nn[[j, k]], {j, 4}, {k, 4}]

• Do makes more sense here than Table. May 4, 2019 at 10:03