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Re: How to deal with this message?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg112623] Re: How to deal with this message?
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Thu, 23 Sep 2010 04:22:51 -0400 (EDT)

On 9/22/10 at 1:56 AM, olfa.mraihi at yahoo.fr (olfa) wrote:

>when trying to solve a system of equations I have obtained this
>message :

>Reduce::useq: The answer found by Reduce contains unsolved
>equation(s) {...}. A likely reason for this is that the solution set
>depends on branch cuts of Mathematica functions.

>Could someone help me to understand in simple terms this message
>(especially branch cuts and dependency on them) and how to find
>solution to avoid this message.

A function with a branch cut is one that exhibits a
discontinuity. For example, the square root function exhibits
such a discontinuity when fed complex values. That is

In[1]:= {Sqrt[-1 + 0.01 I], Sqrt[-1 - 0.01 I]}

Out[1]= {0.00499994 + 1.00001 I, 0.00499994 - 1.00001 I}

Many mathematical functions exhibit similar behavior for some
points in the complex plane.

As for avoiding problems with branch cuts, I've no way to
provide meaningful suggestions until you provided details of
what it is you are trying to do when you got the error message.



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