Multiplying Elements of arrays: Inner product

• To: mathgroup at smc.vnet.net
• Subject: [mg68497] Multiplying Elements of arrays: Inner product
• From: Gopinath Venkatesan <gopinathv at ou.edu>
• Date: Tue, 8 Aug 2006 06:28:31 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```I have to dot multiply cd (3x3 matrix) by ab (3x1 column vector). Also I defined values for the first row and the diagonal elements of cd matrix, as well as defined the column vector ab with values. Now ab = {1, 2, 3}, and cd = {{1, 2, 3}, {b[2,1], 1, b[2,3]}, {b[3,1], b[3,2], 1}}.

I expect the ef to be {14, 2+b[2,1]+3b[2,3], 3+b[3,1]+2b[3,2]} column vector. But it returns the first element in unevaluated form as 1.1+2.2+3.3. Why is this so? How to make it evaluate them? Thanks for the suggestions. Please see below for my example.

ab = Array[a, 3];
cd = Array[b, {3, 3}];
ef = Array[c, 3];
Do[cd[[i, i]] = 1, {i, 1, 3}];
cd[[1, 2]] = 2;
cd[[1, 3]] = 3;
Do[ab[[i]] = i, {i, 1, 3}];
Do[ef[[i]] = 0, {i, 1, 3}];
Do[ef[[i]] = ef[[i]] + cd[[i, k]].ab[[k]], {i, 1, 3}, {k, 1, 3}];

Gopinath

```

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