Re: [GiNaC-list] GiNaC::marix::solve(..)

3 Jun 2009

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Message: 1
Date: Tue, 02 Jun 2009 18:37:08 +0200
From: Lisa Maletzki <l.maletzki@tu-bs.de>
Subject: [GiNaC-list] GiNaC::marix::solve(..) problem
To: ginac-list@ginac.de
Message-ID: <20090602183708.y2zyinropw4o840k@webmail.tu-bs.de>
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Hey,
I have a smallish problem with the method mentioned above
(matrix::solve(..)). I have two nxn numeric matrices A and b (from the
equation Ax=b) and of course want the matrix x in the end but I keep
on getting the error that the first argument must be a matrix of
symbols. Now my question how can I do that? I tried it with ex
symbolic_matrix(..) but I couldn't get it to work since it is of the
type ex and not matrix.
Kind regards,
Lisa
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Message: 2
Date: Tue, 02 Jun 2009 19:35:08 +0200
From: Jens Vollinga <jensv@nikhef.nl>
Subject: Re: [GiNaC-list] GiNaC::marix::solve(..) problem
To: GiNaC discussion list <ginac-list@ginac.de>
Message-ID: <4A2562CC.2020405@nikhef.nl>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi,
Lisa Maletzki schrieb:
...
I have a smallish problem with the method mentioned above
(matrix::solve(..)). I have two nxn numeric matrices A and b (from the
equation Ax=b) and of course want the matrix x in the end but I keep on
getting the error that the first argument must be a matrix of symbols.
Now my question how can I do that? I tried it with ex
symbolic_matrix(..) but I couldn't get it to work since it is of the
type ex and not matrix.
take the following example as a guide:
matrix A(2,2);
  A = 1, 2, 3, 4;
  symbol x1("x1"), x2("x2");
  matrix x(2,1);
  x = x1, x2;
  matrix b(2,1);
  b = 5, 6;
  cout << A.solve(x, b) << endl;
As the manual warns, you will get an exception thrown if the system is
overdetermined. A more robust version is shown in the following example
using no matrices:
symbol x1("x1"), x2("x2");
  lst equations;
  equations.append(1*x1 + 2*x2 == 5);
  equations.append(3*x1 + 4*x2 == 6);
  cout <<  lsolve(equations, lst(x1,x2)) << endl;
Regards,
Jens
Thank you Jens. But the problem I have is, that I do not know how big  
my matrix will be. In the smallest case it is a 18x18 matrix, so  
getting all those symbols would be rather complicated, or am I just  
thinking that?

Kind regards,

Lisa