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Re: Symbolic manipulation with Sqrt[-1] ?
Posted:
Dec 7, 2009 11:20 AM
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Axel Vogt schrieb:
>
> In Maple (which - to answer your latter question - is not free of
> strange behaviours):
>
> eval( (a+b*I)/(c-I*d), I=-I );
>
> a - b I
> -------
> c + d I
>
> There is a (non-recursive) command 'substitute' as well, it would do
> here.
>
> For the other example given by Richard Fateman:
>
> simplify( x^2, {x^2=y^4} );
> 4
> y
>
> This is called 'simplification with side relations' (=w.r.t
> equations).
>
> It however would not work for simplify( 1/sqrt(x^3), {sqrt(x^3)=y} ),
> the command needs polynomial relations.
>
> And it does not work for constants like simplify( 1/sqrt(2), {2=y^2}
> ).
Do I understand you correctly that it is impossible in Maple to
substitute something for arbitrary subexpressions? Are only variables
(and predefined constants like I) allowed? Would
eval( 1/x^2, x^2 = y^4 );
or
eval( 2*cos(x^2), cos(x^2) = sin(y) );
be forbidden syntactically?
Martin.
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