       Re: Table to calculate faster

• To: mathgroup at smc.vnet.net
• Subject: [mg122401] Re: Table to calculate faster
• From: Jacopo Bertolotti <jacopo.bertolotti at gmail.com>
• Date: Thu, 27 Oct 2011 06:32:44 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201110262138.RAA00042@smc.vnet.net>

```Maybe it's just me but it looks like the definition of each T[n,t]
depends on the evaluation of the matrix itself on a previous time and so
on iteratively. Since the code does not include any starting condition
at t==0 all three definition enter a infinite loop preventing any useful
evaluation.

Best regards

Jacopo

On 10/26/2011 11:38 PM, Michelle Maul wrote:
> I am trying to perform a heat transfer calculation on a wall with
> transient heating.  I am using rules so that we can easily change the
> material.  I want to be able to do several hundred time steps but I am
> only able to get about 10 in an hour.  It is a pretty straight forward
> calculation so I'm wondering why it is taking so long to compute.
> This is a calculation that Excel would be good at because it is taking
> data from the cells above it to solve.  Help please
>
> T[0, t_] := (1. -
>         2. \[Tau] - (2. \[Tau] Subscript[h, in] \[CapitalDelta]x)/k) T[
>        0, t - 1] +
>      2. \[Tau] T[1,
>        t - 1] + (2. \[Tau] Subscript[h, in] \[CapitalDelta]x)/k*
>       Subscript[T, in] /. masonry;
>
> T[m_, t_] := \[Tau] (T[m - 1, t - 1] + T[m + 1, t - 1]) + (1. -
>         2. \[Tau]) T[m, t - 1] /. masonry;
>
> T[5, t_] := (1. - 2. \[Tau] -
>         2. \[Tau] (Subscript[h, out] \[CapitalDelta]x)/k) T[5,
>        t - 1] + 2. \[Tau] T[4, t - 1] +
>      2. \[Tau] (Subscript[h, out] \[CapitalDelta]x)/
>       k*(Subscript[T, out] /. {x ->  t}) +
>      2. \[Tau] (\[Kappa] *(Subscript[q,
>          solar] /. {x ->  t}) \[CapitalDelta]x)/k /. masonry;
>
> solution = Transpose[Table[T[n, x], {n, 0, 5}, {x, 0, 24}]]
>
> Thank you
>
>

```

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