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MathGroup Archive 2004

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Re: Syntax Questions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg50749] Re: [mg50731] Syntax Questions
  • From: Murray Eisenberg <murray at math.umass.edu>
  • Date: Sun, 19 Sep 2004 03:55:55 -0400 (EDT)
  • Organization: Mathematics & Statistics, Univ. of Mass./Amherst
  • References: <200409180948.FAA00552@smc.vnet.net>
  • Reply-to: murray at math.umass.edu
  • Sender: owner-wri-mathgroup at wolfram.com

First, probably you ought to put the resulting matrix T in the form {{a, 
b}, {c, d}}, since that would seem to be consistent with the matrix of 
coefficients of the two linear equations.  What you have is, of course, 
the transpose of that.

You could do it like this:

   m = {{a, b}, {c, d}};
   m /. First @ Solve[m . {v1, v2} == {u1, u2}, Flatten[m]]
{{u1/v1 - (b*v2)/v1, b}, {u2/v1 - (d*v2)/v1, d}}

I show the InputForm of the actual StandardForm result displayed by 
Mathematica.

(You still obtain a warning message "Equations may not give solutions 
for all 'solve' variables.")


Dominik Werder wrote:

> While trying real easy Calculations with mathematica 5 on solaris I  
> encountered difficulties finding the right syntax:
> 
> Here I try solve some equations and write the four resulting variables  
> a,b,c,d into a new matrix T:
> 
> s = Solve[{u1 == a v1 + b v2, u2 == c v1 + d v2}, {a, b, c, d}];
> a = (a /. s)[[1]];
> b = (b /. s)[[1]];
> c = (c /. s)[[1]];
> d = (d /. s)[[1]];
> T = {{a, c}, {b, d}};
> 
> I'm sure this could be done easier, but I dont know how?
> 
> thanks!
> Dominik
> 
> 

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower      phone 413 549-1020 (H)
University of Massachusetts                413 545-2859 (W)
710 North Pleasant Street            fax   413 545-1801
Amherst, MA 01003-9305


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