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# Re: [xsl] Increasing sequence ?

 Subject: Re: [xsl] Increasing sequence ? From: "Michael Kay mike@xxxxxxxxxxxx" Date: Fri, 27 Mar 2015 11:05:35 -0000

```What we're seeing here is that the best solution is radically influenced by
the optimization strategies within the processor.

Dimitre's recursive approach is only worth doing if the processor has
non-constant performance for an expression of the form sequence[\$N] where \$N
is an integer; that is, if sequences are implemented as linked lists rather
than arrays. Saxon will generally use an adaptive implementation where the
sequence is held as an array as soon as you start indexing into it, so the
non-recursive solution will work just fine. Other systems may differ.

Then, if you do use the recursive approach, you run into problems if the
processor doesn't do tail-call optimization. And if that's the case, you need
to consider a divide-and-conquer approach instead.

Michael Kay
Saxonica
mike@xxxxxxxxxxxx
+44 (0) 118 946 5893

On 27 Mar 2015, at 09:36, Leo Studer leo.studer@xxxxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

> Dimitre
>
> thanks, this is amazing. With Saxon EE in Oxygen 16.1 I get stack overflow
with 10000 ;-).
> Can you compare the time with this solution?
> declare namespace my = "my:my";
> declare function my:increasing2(\$seq as xs:double*)as xs:boolean
> {every \$v in 1 to (count(\$seq)-1) satisfies (\$seq[\$v] lt \$seq[\$v+1])};
> let \$v:=(1 to 1000000) return (my:increasing2(\$v))
>
> Cheers
> Leo
>
>> On 27.03.2015, at 05:24, Dimitre Novatchev dnovatchev@xxxxxxxxx
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>>
>> Hi Leo,
>>
>> I ran this with BaseX 7.8.2:
>>
>> declare namespace my = "my:my";
>> declare function my:increasing(\$seq as xs:double*) as xs:boolean
>> {empty(\$seq[2])
>> or
>>  \$seq[1] lt \$seq[2]  and  my:increasing(subsequence(\$seq, 2))
>> };
>> let \$v:=(1 to 10000)
>>  return my:increasing(\$v)
>>
>>
>> And here is the result (do note this below: - marking as ***tail
>> call***: my:increasing(fn:subsequence(\$seq_0, 2))  )
>>
>> Total Time: 3.74ms (for 100 000 - long sequence the time was 17.77ms,
>> for 1 000 000 - long sequence the time was 207.56ms)
>
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