I have a small problem where I remember I learned it in the past. But now I can't seem to recall how to do it. I searched on google, but I think even though it is probably really easy, I may not have worded it right to get the references I want. So I decided to ask here. Here is the problem: Lets say I have this 4x3 matrix: [1,2,3;5,6,7;9,0,1;3,4,5] What matrix can I multiply this with or by to get back, for this example, 1&2 in the first row and 6&7 in the second row and the rest should be zero...? Now what is that general structure I need to make the second matrix to get back or be able to "pick off" any value from the first matrix that I choose..? I know this is an easy question but I don't have my Math Physics book with me and I'm terrible at wording what I need to ask. Haha. Thanks in advance.