Re: Optimizing For loop statement

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• Subject: [mg129884] Re: Optimizing For loop statement
• From: David Bailey <dave at removedbailey.co.uk>
• Date: Fri, 22 Feb 2013 01:06:04 -0500 (EST)
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```On 21/02/2013 03:26, tarpanelli at libero.it wrote:
> Hello, here below you can find a piece of Mathematica code:
> ...
> For[i=3,i<=n,i++,
> s=sigma[a,b,c]
> vol=ReplacePart[vol,{{i,1}->x[[i]],{i,2}->s}];
> Clear[b];
> b=Interpolation[vol];
> ];
>
> where sigma is a module which take as input parameters two scalars (a,c) and one interpolating function (b).
> What I need is to update the data (vol), on which the interpolating function is built, according to the new result of the module sigma which takes, itsself, the interpolating function as input parameter.
>
> I see that the For loop statement is really time-consuming, and I would like to know if it is possible to ptimize it.
> thanks a lot
> Paolo
>
>
People will tell you not to use For because it is slower than using
functional constructs, but that is not the main problem here. You don't
want to use ReplacePart to update vol, use something like:

vol[[i]]={x[[i]],s};

Also, you don't need to Clear b before giving it a value! Clearing could
well be expensive too.

David Bailey
http://www.dbaileyconsultancy.co.uk

```

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