Sorry. i forgot to mention that the bug was observed in version 4.3.3
(from source tarball, fresh install) on a (rather untouched)
lenny/2.6.26-amd46.
regards
felix
On Tue, Mar 16, 2010 at 02:42:19PM +0100, Felix Salfelder wrote:
> Hi all.
>
> I just encountered something like a bug, when i tried to calculate some
> statistics.
>
> here is an example:
> \begin{example}
> var('x s')
> assume(x>0)
> S=x.parent()
> w0=S.wild(0)
> f(x) = (2/sqrt(pi)*exp(-s^2)).integrate(s,0,x)
> g(x) = f(x).diff(x)
> h(x) = diff(erf(x),x)
> print "g :", g
> print "h :", h
> print "g :", g.subs(diff(erf(x),x)(x=w0) == 2/sqrt(pi) * exp(-w0^2))
> print "h :", h.subs(diff(erf(x),x)(x=w0) == 2/sqrt(pi) * exp(-w0^2))
> print "g-h :", g-h
> print "g-h :",(g-h).subs(diff(erf(x),x)(x=w0) == 2/sqrt(pi) * exp(-w0^2))
> print "g-h :",(g-h).simplify()
> \end{example}
>
> the output is as follows:
> \begin{output}
> 1: g : x |--> D[0](erf)(x)
> 2: h : x |--> D[0](erf)(x)
> 3: g : x |--> D[0](erf)(x)
> 4: h : x |--> 2*e^(-x^2)/sqrt(pi)
> 5: g-h : x |--> -D[0](erf)(x) + D[0](erf)(x)
> 6: g-h : x |--> -2*e^(-x^2)/sqrt(pi) + D[0](erf)(x)
> 7: g-h : x |--> 0
> \end{output}
>
> I dont understand why output line 3 differs from output line 4.
> in line 5-7 simplify() works as expected, but subs() doesnt.
>
> regards and thanks
> felix
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