On Tue, 29 Nov 2011 13:14:36 -0700
[email protected] wrote:
> Hi! I'm working with an expression involving imaginary exponentials
> and their conjugates:
>
> exp(i•k•x)
>
> exp(i•k•x)*=exp(-i•k•x)
>
> However, when multiplying them together, I do not get the arguments
> to evaluate to zero. My variables x and k are real, and I've told
> sage to assume that they are real. But it will not evaluate:
>
> exp(i•k•x)•(exp(i•k•x))*
>
> as:
>
> exp(i•k•x+(i•k•x)*)=exp(i•k•x+(i*•k*•x*))=exp(i•k•x+(-i•k•x))=exp(i•k•x-i•k•x)=exp(0)=1.
>
>
> Any ideas?
Try this:
sage: var('x',domain=RR)
x
sage: var('k',domain=RR)
k
sage: exp(i*x*k)
e^(I*k*x)
sage: exp(i*x*k)*exp(-i*x*k)
1
The assume() system is from maxima. Unfortunately, basic arithmetic with
symbolic expressions doesn't know about these. It uses a different
system as you can see.
There must be a ticket to make these two assumption systems play nice,
but I can't find it ATM.
Cheers,
Burcin
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