       Re: Bug in Convolve, version 7

• To: mathgroup at smc.vnet.net
• Subject: [mg98381] Re: Bug in Convolve, version 7
• From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
• Date: Wed, 8 Apr 2009 05:04:04 -0400 (EDT)
• References: <grhhb2\$j39\$1@smc.vnet.net>

```Hi Daniel,

Looks like a genuine bug. I found another one with Convolve:

Convolve[Sin[x], Cos[x], x, y]

Mathematica thinks it's 0, whereas the integral doesn't converge.
Interestingly, it doesn't report a result on the commuted version:

Convolve[Cos[x], Sin[x], x, y]

Cheers -- Sjoerd

On Apr 8, 8:48 am, dh <d... at metrohm.com> wrote:
> Hello,
>
> convolution is commutative, f*g == g*f.
>
> now consider the 2 calulations, where we simply exchange the first 2
>
> arguments of Convolve:
>
> f = UnitBox;
>
> Convolve[f[x1], f[x1], x1, x2]
>
> Convolve[%, f[x2], x2, x3]
>
> Convolve[%, f[x3], x3, x4]
>
> Plot[%, {x4, -2, 2}]
>
> f = UnitBox;
>
> Convolve[f[x1], f[x1], x1, x2]
>
> Convolve[f[x2], %, x2, x3]
>
> Convolve[f[x3], %, x3, x4]
>
> Plot[%, {x4, -2, 2}]
>
> wheras the first calculation is correct, the second is obviously wrong.
>
> Daniel
>
> P.S. i tried this with version 7.0.1 and Windows

```

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