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Different answer when running cell second time?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109692] Different answer when running cell second time?
  • From: Jason Quinn <jason.lee.quinn at gmail.com>
  • Date: Wed, 12 May 2010 07:33:19 -0400 (EDT)

If I open Mathematica 7.01.0 (64-bit Linux version) that only contains
the following input in a single cell,

Assuming[\[Sigma] > 0, Integrate[p/((Pi*\[Sigma]^2)*E^((p^2 -
2*p*p0*Cos[2*(\[Phi] - \[Phi]0)] + p0^2)/(2*\[Sigma]^2))),  {p0, 0,
Infinity}]]

When I hit shift-enter, I get an answer. If I hit, shift-enter a
second time, I get a different answer. Can anybody tell me why? This
seems like a bug. It happens even if I clear all the variables used in
the calculation.

Jason

PS This version of Mathematica on Linux has been extremely buggy for
me. Abort and Interrupt do not work properly. Mathematica crashes very
frequently and seems to revert my documents back to the state they
when when I opened Mathematica even if I have saved in the mean time.
Palletes and other floating popups do not function properly with the
window manager on Ubuntu and sometimes have no title bar or other
means to move them around.

PPS The two answers are

(E^(-((p^2 Sin[2 \[Phi] - 2 \[Phi]0]^2)/(
  2 \[Sigma]^2))) p (Sqrt[p^2 Cos[2 \[Phi] - 2 \[Phi]0]^2] +
   p Cos[2 \[Phi] - 2 \[Phi]0] Erf[Sqrt[(
     p^2 Cos[2 \[Phi] - 2 \[Phi]0]^2)/\[Sigma]^2]/Sqrt[
     2]]))/(Sqrt[\[Pi]] \[Sigma] Sqrt[
 p^2 (1 + Cos[4 \[Phi] - 4 \[Phi]0])])



and


(E^(-((p^2 Sin[2 \[Phi] - 2 \[Phi]0]^2)/(
  2 \[Sigma]^2))) p (1 +
   Erf[(p Cos[2 \[Phi] - 2 \[Phi]0])/(Sqrt[2] \[Sigma])]))/(Sqrt[
 2 \[Pi]] \[Sigma])



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