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MathGroup Archive 2007

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Re: Re: Weird result in Mathematica 6


  Applying ComplexExpand[] to real assumptions and ComplexExpand[ , 
{x}] to complex ones will normally avoid such problems:

Simplify[Im[x], Assumptions -> {ComplexExpand[x - Conjugate[x] > 0,  
{x}]}]
  Im(x)

Andrzej Kozlowski

On 24 May 2007, at 19:18, Sebastian Meznaric wrote:

> Another related effect can be used to actually derive contradictions
> in Mathematica. Try this
> Simplify[Im[x],Assumptions->{x-Conjugate[x]>0}]
>
> It returns 0. The assumption was that Im[x]>0 so here Mathematica
> clearly contradicts the assumption.
>
> Obviously this suggests one should be very careful when using
> inequalities with complex quantities. I think this sort of bugs should
> really be fixed considering how much trouble Mathematica usually goes
> into to ensure that real quantities are not assumed in expressions.
>
>



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