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