       Re: Problems with solving integrals in Mathematica 9

• To: mathgroup at smc.vnet.net
• Subject: [mg131002] Re: Problems with solving integrals in Mathematica 9
• From: Andrzej Kozlowski <akozlowski at gmail.com>
• Date: Sun, 2 Jun 2013 00:30:34 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• Delivered-to: l-mathgroup@wolfram.com
• Delivered-to: mathgroup-outx@smc.vnet.net
• Delivered-to: mathgroup-newsendx@smc.vnet.net
• References: <20130601102628.B6E6B69C7@smc.vnet.net>

```In my opinion Mathematica is right.

Try the indefinite integral:

Integrate[f'[x]/f[x], x]

Log[f[x]]

No problem. Now, you claim that the correct answer for the definite
integral is -Log[f] + Log[f[T]] but obviously this depends on various
assumptions on f. Simply by taking f(x)=x you will get a
non-convergent integral:

f[x_] := x
Integrate[f'[x]/f[x],{x,0,T}]
During evaluation of In:= Integrate::idiv: Integral of 1/x does
not converge on {0,T}. >>
Integrate[1/x, {x, 0, T}]

Mathematica attempts to give an answer with full generality (expect
perhaps for non-generic cases) and in this no such answer can be given.
Thus, I would argue, this actually represents a fix of a bug in
Mathematica 8.

Andrzej Kozlowski

> Has anybody encountered the same problems with solving integrals in
Ver. 9 as I did?
>
> Here a very simple example:
>
> Integrate[D[f[x], x] / f[x], {x, 0, T}]
>
> Version 8.04 gives the correct results:
>
> -Log[f] + Log[f[T]]
>
> In Version 9.00 as well as 9.01 this integral can't be solved. With
more complicated integrals I had the same problems. Version 8 gives a
solution, Version 9 doesn't!
>
> Could some other Version 9 users try it.
>

```

• Prev by Date: Re: defining a function whose parameter must be a function with two
• Next by Date: Re: defining a function whose parameter must be a function
• Previous by thread: Problems with solving integrals in Mathematica 9
• Next by thread: Re: Problems with solving integrals in Mathematica 9