MathGroup Archive 2009

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: expression form


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
>>
>>
>>
>>



  • Prev by Date: Re: Integrate[], Sort[] and Hold[]
  • Next by Date: Re: BarChart and Ticks
  • Previous by thread: Re: expression form
  • Next by thread: Re: expression form