Re: Compile question

• To: mathgroup at smc.vnet.net
• Subject: [mg73916] Re: Compile question
• From: dh <dh at metrohm.ch>
• Date: Sat, 3 Mar 2007 00:59:53 -0500 (EST)
• References: <es6d6h\$rq1\$1@smc.vnet.net>

```
Hi Ray,

if you replace the empty list in the Last If[..] by e.g.: {-1} it works

as expected. Why this is so I can only guess. Presumably, a compiled

function must always return the same type of expression. And an empty

array may be regarded as an empty array of reals.

Daniel

Ray Koopman wrote:

> I've been trying different ways to "walk the list" as suggested in

> the recent thread "split again". Here is some uncompiled code that

> works as I expected, but the compiled version returns reals instead

> of integers. Does anyone know why?

>

> SeedRandom[2]; z = Table[Random[],{20}]

>

> {0.238705,0.844529,0.473928,0.421515,0.512692,

>  0.0228035,0.529257,0.0507012,0.74907,0.632356,

>  0.0725195,0.251276,0.902785,0.672727,0.419794,

>  0.512577,0.404555,0.00984124,0.168643,0.50482}

>

> s4[z_,a_,b_] := Module[{n = Length@z, j = 0, k}, k = n;

> Do[If[ z[[i]] >= a, If[ i <= j+b+1, j = i, k = i-1; Break[]]], {i,n}];

> If[ k <= j+b, {}, {j+1,k} ] ]

>

> s4[z,.7,5]

> s4[z,.7,6]

> s4[z,.7,7]

>

> {3,8}

> {14,20}

> {}

>

> s4c = Compile[{{z,_Real,1},{a,_Real},{b,_Integer}},

> Module[{n = Length@z, j = 0, k}, k = n;

> Do[If[ z[[i]] >= a, If[ i <= j+b+1, j = i, k = i-1; Break[]]], {i,n}];

> If[ k <= j+b, {}, {j+1,k} ] ],

> {{n,_Integer},{j,_Integer},{k,_Integer},{i,_Integer}} ];

>

> s4c[z,.7,5]

> s4c[z,.7,6]

> s4c[z,.7,7}

>

> {3.,8.}

> {14.,20.}

> {}

>

>

```

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