       Re: functional programming

• To: mathgroup at smc.vnet.net
• Subject: [mg63017] Re: functional programming
• Date: Sun, 11 Dec 2005 04:56:38 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```On 12/10/05 at 6:02 AM, mike_in_england2000 at yahoo.co.uk wrote:

>As a long time C++ programmer I am terrible at functional
>programming. I recently replied to a post on here concerning
>diophantine equations and provided the following code:

>dioph[x_, k_] := (5 x)^2 - 2^k*3*(5 + k)^2 - 131*k - 7
>Reap[
>  Do[
>    Do[
>      If[dioph[x, k] == 0, Sow[{x, k}];];
>      , {x, 0, 1000}
>      ]
>    , {k, 0, 1000}
>    ]]

>How could I have rewritten my orginal code using Functional
>programming?

>I tried

>dioph[x_, k_] := If[(5 x)^2 - 2^k*3*(5 + k)^2 - 131*k - 7 == 0, {x,
>k}]; Table[dioph[x, k], {x, 0, 10}, {k, 0, 10}];

Here is one approach

Cases[
Flatten[
Table[{x, k, (5*x)^2 - 2^k*3*(5 + k)^2 - 131*k - 7}, {x, 50},
{k, 50}],
1],
{__, 0}]

{{31, 6, 0}}

Another approach would be

dioph[x_, k_] := (5*x)^2 - 2^k*3*(5 + k)^2 - 131*k - 7

Cases[
Flatten[
Outer[{#1, #2, dioph[#1, #2]}&, Range, Range],
1],
{__, 0}]

{{31, 6, 0}}
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```

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