compile speed

• To: mathgroup at smc.vnet.net
• Subject: [mg74421] compile speed
• From: "Boson" <sandro.romani at gmail.com>
• Date: Wed, 21 Mar 2007 02:43:04 -0500 (EST)

```dear mathematica users,

i've written a simple function that works on a pair of binary
matrices:
(mathematica 5.2 linux, on a 32 bit platform)

tab[nx_, ny_, frac_] := Table[If[Random[] < frac, 1, 0], {nx}, {ny}]

nx = 25; ny = 50; frac1 = 0.1; frac2 = 0.5;
p1 = 0.4; p2 = 0.2;
tabrect = tab[nx, ny, frac1];
tabsq = tab[ny, ny, frac2];

testnocomp[mat1_, mat2_, n1_, n2_, pp1_, pp2_] := Module[{tmp, sum,
val},
tmp = mat2; Do[sum = mat1[[k,j]] + mat2[[k,i]];
val = Which[sum == 2, If[Random[] < pp1, 1, tmp[[i,j]]], sum ==
1,
If[Random[] < pp2, 0, tmp[[i,j]]], sum == 0, tmp[[i,j]]];
tmp[[i,j]] = val,
{k, n1}, {i, n2}, {j, n2}]; tmp];

Timing[resnc = testnocomp[tabrect, tabsq, nx, ny, p1, p2]; ]

the result of the timing is
{0.7558840000000013*Second, Null}

since i need high values of nx,ny (~5000) and the loop scales as
nx*ny^2,
i tried to implement a compiled version of the previous function:

test := Compile[{{mat1, _Integer, 2}, {mat2, _Integer, 2}, {n1,
_Integer}, {n2, _Integer},
{pp1, _Real}, {pp2, _Real}}, Module[{tmp, sum, val},
tmp = mat2; Do[sum = mat1[[k,j]] + mat2[[k,i]];
val = Which[sum == 2, If[Random[] < pp1, 1, tmp[[i,j]]], sum
== 1,
If[Random[] < pp2, 0, tmp[[i,j]]], sum == 0, tmp[[i,j]]];
tmp[[i,j]] = val,
{k, n1}, {i, n2}, {j, n2}]; tmp], {{Random[_], _Real}}];

Timing[res = test[tabrect, tabsq, nx, ny, p1, p2]; ]

results are a disaster:
{14.814747999999996*Second, Null}

i'm sure this is related to my poor mathematica programming
experience..

could you suggest me a faster version to solve this problem?

regards,
sandro

```

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