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Re: expression form

  • To: mathgroup at smc.vnet.net
  • Subject: [mg101008] Re: [mg100997] expression form
  • From: Haibo Min <yshdfeng at gmail.com>
  • Date: Sat, 20 Jun 2009 04:02:20 -0400 (EDT)
  • References: <200906200048.UAA00953@smc.vnet.net>

Thank you for your time and advice, Mr. Matthias Bode.

It does work in this simple case. However, It still doesn't work when the
elements in vector or matrix is a little bit complicated.
For example,
when P={{Subscript[k, p], -Subscript[m, f] Subscript[\[Epsilon], 1],
  0}, {-Subscript[m, f] Subscript[\[Epsilon], 1], Subscript[m,
  f], -Subscript[m, f] Subscript[\[Epsilon],
   1]}, {0, -Subscript[m, f] Subscript[\[Epsilon], 1], Subscript[k,
  d]/b}},
and a={{Subscript[e, p]}, {Subscript[e, v]}, {\[CurlyTheta]}}

Using your method: Transpose[a].P
the result is still: Transpose[a].P
But the weird thing is, when P is less complicated, say,
P = {{Subscript[k, p], Subscript[m, f], 0}, {Subscript[m, f],
   Subscript[m, f], Subscript[m,
   f]}, {0, -Subscript[\[Epsilon], 1] Subscript[m, f], Subscript[k,
   d]/b}}
still using Transpose[a].P or just a.P
they both work!

I am wondering why? Is there a specific setting command which requires the
results are explicit expressions?

Best regards,

Haibo Min


On Sat, Jun 20, 2009 at 10:10 AM, Matthias Bode <lvsaba at hotmail.com> wrote:

> Hello Mr. Haibo Min:
>
> INPUT:
> Clear[a, p]
> a = {{a1}, {a2}, {a3}};
> p = {{p11, p12, p13}, {p21, p22, p23}, {p31, p32, p33}};
> Transpose[a] . p
>
> OUTPUT:
> {{a1*p11 + a2*p21 + a3*p31, a1*p12 + a2*p22 + a3*p32, a1*p13 + a2*p23 +
> a3*p33}}
>
> Is this the result you intended?
>
> Best regards,
>
> MATTHIAS BODE
> Las Lomas de Aranjuez
> COCHABAMBA/BOLIVIA
> --------------------------------------------------
> From: "Haibo Min" <yshdfeng at gmail.com>
> Sent: Saturday, June 20, 2009 12:48 AM
> To: <mathgroup at smc.vnet.net>
> Subject: [mg100997] expression form
>
>
> Hi, I am fairly new to mathematica, and I have a question on the matrix
>> multiplication operator.
>>
>> Suppose a={a1,a2,a3},P={{p11,p12,p13},{p21,p22,p23},{p31,p32,p33}}. I want
>> to get the explicit expression of a'Pa, where a' is the transpose of
>> vector
>> a. Since there is no "transpose" concept for vector, my expression in
>> mathematica is
>> a.P.a
>> However, it just
>> returns {a1,a2,a3}.{{p11,p12,p13},{p21,p22,p23},{p31,p32,p33}}.{a1,a2,a3},
>> seems nothing is done about this, why?
>> I use mathematica v7.0
>>
>> Thank you!
>>
>> Haibo Min
>> yshdfeng at gmail.com
>>
>>
>>
>>



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