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MathGroup Archive 2007

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Re: Solving a symbolic complex linear system of equation.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg77944] Re: Solving a symbolic complex linear system of equation.
  • From: Szabolcs <szhorvat at gmail.com>
  • Date: Wed, 20 Jun 2007 05:33:23 -0400 (EDT)
  • Organization: University of Bergen
  • References: <f58dlb$8lc$1@smc.vnet.net>


Please state the question precisely.

Fo wrote:
> Suppose that I want to solve symbolically a system of lienar equations
> defines as:
> $Ax=B$ , where A is a complex matrix, B is a complex vector and x is
> the vector of the unkown.

You say you want to solve A x = B.  If A is invertible, the solution is 
x = A^-1 B.  Inverse[] can be used to compute A^-1.

> The elements of the A matrix (that is simmetric) are in the form
> $A_{ij}e^{i phi_{ij}}$.
> I tried in several ways but I couldn't define the variables $A_{ij}$
> and $ phi_{ij}$ as real.

Any complex number can be written in the form A Exp[I*phi] (where A and 
phi are real), so I do not see the point here.

Or is a '=' sign missing and you mean that all the elements are complex 
numbers of magnitude 1?  Even if they are, the solution is still A^-1 B.

Do you mean that you would like to specify that some of the variables 
are real when simplifying the end result? For this, look up the syntax 
for Simplify[], and use something similar to Simplify[Sqrt[a^2], a 
\[Element] Reals] to specify that a variable 'a' is real.

> I tried using the package Algebra`ReIm` and to define each variable as
> z/:Im[z]=0.
> But it does not the wanted result and also I've already read the help
> page for ComplexExpand[].

What kind of result do you expect?  It would be helpful if you posted 
the complete problem, with some more detailed explanation.

> Thank you, every suggestion will be helpful.
> Fortu
> 
> 


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