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Re: How to declare vectors for solving

  • To: mathgroup at smc.vnet.net
  • Subject: [mg106504] Re: How to declare vectors for solving
  • From: Norbert Marxer <marxer at mec.li>
  • Date: Fri, 15 Jan 2010 03:16:02 -0500 (EST)
  • References: <hik907$6mo$1@smc.vnet.net>

On Jan 13, 11:58 am, John Rivers <firs... at btinternet.com> wrote:
> currently I do this:
>
> a = {ax, ay, az};
> b = {bx, by, bz};
>
> then I can work with Cross[a, b] etc.
>
> and then Solve[]
>
> is there a way to declare a as a vector with 3 elements - but not give
> values?

Hello

I do not know exactly what you want to do, but maybe this helps.

If you define your vectors (here given in InputForm, the expression
looks nice in StandardForm) in the following way:

     OverVector[x_] = {Subscript[x, 1], Subscript[x, 2], Subscript[x,
3]};

The you can (without defining a and b) take the cross product:

     Cross[OverVector[a], OverVector[b]]

Or you can use these vectors in Solve:

     Solve[{OverVector[c] + OverVector[b] == {1, 2, 3},
         OverVector[a] + OverVector[b] == {2, 3, 4},
         OverVector[a] + OverVector[c] == {1, 7, 4}},
         Flatten[{OverVector[a], OverVector[b], OverVector[c]}]]

Best Regards
Norbert Marxer





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