Constructing matrix out of submatrices

*To*: mathgroup at smc.vnet.net*Subject*: [mg113776] Constructing matrix out of submatrices*From*: Sebastian Schmitt <sschmitt at physi.uni-heidelberg.de>*Date*: Fri, 12 Nov 2010 05:26:54 -0500 (EST)

Hi! I would like to construct a matrix out of submatrices. I guess this is straight forward but somehow I couldn't find the correct way in the documentation. The example that follows is of course simplified. Please don't take shortcuts. I start with a zero matrix and a submatrix: matrix = ConstantArray[0, {3, 3}] submatrix = {{a, b}, {c, d}} I want to specificy the upper-left corner in the matrix where the submatrix should be placed. If the position is {1,1} the result should be: result = {{a, b, 0}, {c, d, 0}, {0, 0, 0}} If it is {1,2}: result = {{0, a, b}, {0, c, d}, {0, 0, 0}} etc. ReplacePart together with ArrayFlatten comes close, but the submatrix does not "override" zeros: ReplacePart[matrix, {1, 1} -> submatrix] // ArrayFlatten {{a, b, 0, 0}, {c, d, 0, 0}, {0, 0, 0, 0}, {0, 0, 0, 0}} What are possible solutions? Thanks, Sebastian