A question of matrix multiply, who can solve it?

• To: mathgroup at smc.vnet.net
• Subject: [mg25671] A question of matrix multiply, who can solve it?
• From: Chen Jisheng <chenjs at iopp.ccnu.edu.cn>
• Date: Wed, 18 Oct 2000 02:52:38 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```Dear Sir,

As a beginning user, I find a mistake of Mathematic 4.0(/3.0 for student).

That is about the multipy method of matrix.

For example, as I input the two matrices:

A={a[1, 1], a[1, 2], a[1, 3], a[1, 4], a[1, 5]}
{a[2, 1], a[2, 2], a[2, 3], a[2, 4], a[2, 5]}
{a[3, 1], a[3, 2], a[3, 3], a[3, 4], a[3, 5]}
{a[4, 1], a[4, 2], a[4, 3], a[4, 4], a[4, 5]}
{a[5, 1], a[5, 2], a[5, 3], a[5, 4], a[5, 5]},
B={{b[1, 1], b[1, 2], b[1, 3], b[1, 4], b[1, 5]},

{b[2, 1], b[2, 2], b[2, 3], b[2, 4], b[2, 5]},

{b[3, 1], b[3, 2], b[3, 3], b[3, 4], b[3, 5]},

{b[4, 1], b[4, 2], b[4, 3], b[4, 4], b[4, 5]},

{b[5, 1], b[5, 2], b[5, 3], b[5, 4], b[5, 5]}},

then calculate the result of A B. The mathematics gives the following
result:

A B={{a[1, 1] b[1, 1], a[1, 2] b[1, 2], a[1, 3] b[1, 3],

a[1, 4] b[1, 4], a[1, 5] b[1, 5]},

{a[2, 1] b[2, 1], a[2, 2] b[2, 2], a[2, 3] b[2, 3],

a[2, 4] b[2, 4], a[2, 5] b[2, 5]},

{a[3, 1] b[3, 1], a[3, 2] b[3, 2], a[3, 3] b[3, 3],

a[3, 4] b[3, 4], a[3, 5] b[3, 5]},

{a[4, 1] b[4, 1], a[4, 2] b[4, 2], a[4, 3] b[4, 3],

a[4, 4] b[4, 4], a[4, 5] b[4, 5]},

{a[5, 1] b[5, 1], a[5, 2] b[5, 2], a[5, 3] b[5, 3],

a[5, 4] b[5, 4], a[5, 5] b[5, 5]}}.

As all knows, this is not correct. I think it is terrible.

Do you think so? How can improve it?

Looking forward to receiving the reply.

J.-S CHen,
Institute of Particle Physics,
Hua-Zhong Normal University,
Wuhan 430079,China

```

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