       Re: strange behaviour of Integration

• To: mathgroup at smc.vnet.net
• Subject: [mg89055] Re: strange behaviour of Integration
• From: Alois Steindl <Alois.Steindl at tuwien.ac.at>
• Date: Sat, 24 May 2008 03:57:43 -0400 (EDT)
• Organization: Inst. f. Mechanics II, TU Vienna
• References: <g11ra1\$afj\$1@smc.vnet.net>

```Hello,
I just want to add strange results with Mathematica 6.0.1.0:
(I experienced this problem also with 6.0.2)

If I calculate

ih = Integrate[(ri - r)^2/r, {r, rim1, ri},
Assumptions -> {Element[rim1, Reals] && Element[ri, Reals] &&
rim1 > 0 && ri > rim1}]

I get the correct result
-((3 ri^2)/2) + 2 ri rim1 - rim1^2/2 + ri^2 Log[ri/rim1]

But when I divide the integrand by the constant (ri-rim1)^2:

ih2 = Integrate[(ri - r)^2/r/(ri - rim1)^2, {r, rim1, ri},
Assumptions -> {Element[rim1, Reals] && Element[ri, Reals] &&
rim1 > 0 && ri > rim1}]

Mathematica gives
(ri^2 (-3 + 2 Log[ri] - 2 Log[rim1]))/(2 (ri - rim1)^2)

Here the contribution  (2 ri rim1 - rim1^2/2)/(ri-rim1)^2
is simply missing.

How can that happen?

Alois

```

• Prev by Date: Re: Range of Use of Mathematica
• Next by Date: Re: Is it possible to solve this differential equation?
• Previous by thread: Re: strange behaviour of Integration
• Next by thread: Re: fails