
Re: Working with arrays
Posted:
Jun 17, 2013 6:15 AM


On 16/06/2013 10:12, amannucci wrote: > 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 > In the first example, you used CenterDot, which is an operator with no built in meaning. In the second case you used Dot, which will do vector/matrix multiplication!
I must say, I never use these operators, because they can be confused with each other, and a decimal point, and dots also mean repetition in patterns!
David Bailey http://www.dbaileyconsultancy.co.uk

