
Working with arrays
Posted:
Jun 16, 2013 5:12 AM


I thought I understood variables. This sequence completely mystifies me: Clear[lA, xtest] lA = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}; xtest = {4, 5, 6}; lA\[CenterDot]xtest (* First case *) {{a, b}, {c, d}} . {x, y} (* Second case *)
The output is:
{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}\[CenterDot]{4, 5, 6}
{a x + b y, c x + d y}
How do I force matrix multiplication to actually occur, as in the second answer? Why does Mathematica do the matrix multiply in the second case but not the first?
Thanks for any help.
Tony

