Re: 2D Convolution

• To: mathgroup at smc.vnet.net
• Subject: [mg76389] Re: 2D Convolution
• From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
• Date: Mon, 21 May 2007 05:59:16 -0400 (EDT)
• Organization: The Open University, Milton Keynes, UK
• References: <f29389\$m7p\$1@smc.vnet.net><f29bko\$pjn\$1@smc.vnet.net> <f2emd1\$2r6\$1@smc.vnet.net> <f2h96m\$13g\$1@smc.vnet.net>

```Mathieu G wrote:
> CKWong a =E9crit :
>> Errata:
>> g should be the kernel in the function
>>
>> Convolve[f_, g_, x_?NumberQ, y_?NumberQ] := NIntegrate[f[
>>     xPrime, yPrime] *g[x - xPrime,
>>   y - yPrime], {xPrime, -=A1=DB, =A1=DB}, {yPrime, -=A1=DB,=
>  =A1=DB}]
>> Sorry for the snafu.
>>
>>
> Thank you for your replies!!
>
> I have a few questions still since I am neither a mathematician  or a
> mathematica expert:
>
> Is it necessary to use the <?NumberQ> part since using the Convolve
> function for anything else would be non-sense? Does that bring any
> improvement in the Mathematica computation?

The following FAQ should answer your questions: "How do I write a
function which evaluates only when the argument is a number?" Available at
http://support.wolfram.com/mathematica/kernel/features/evalwhennumber.html

Regards,
Jean-Marc

> Why does it make a difference that the kernel is the f or g function?
>
> Best regards,
> MG
>

```

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