RE: [xsl] how to optimize recursive algorithm?

Subject: RE: [xsl] how to optimize recursive algorithm?
From: "Michael Kay" <mhk@xxxxxxxxx>
Date: Thu, 27 Nov 2003 18:06:50 -0000
If you work forwards through the list, you can pass the computed values
onwards as parameters rather than recomputing them each time, which
should make the algorithm O(n) rather than O(n^2).

If you prefer, you can get the caching effect by using memoized
functions in Saxon (saxon:memo-function="yes"), but you have to ask for
this explicitly.

Michael Kay


> -----Original Message-----
> From: owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx 
> [mailto:owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx] On Behalf Of FC
> Sent: 27 November 2003 13:37
> To: XSL-List@xxxxxxxxxxxxxxxxxxxxxx
> Subject: [xsl] how to optimize recursive algorithm?
> 
> 
> Houston, we've got a problem.
> I have a transformation calculating the position of certain 
> graphical elements and each element's position is affected by 
> the position of its ancestors and preceding siblings. The 
> recursive algorithm I wrote works well, meaning that the 
> result is correct but is painfully slow when dealing with big 
> documents. This is no surprise because I am fully aware of 
> the functional language constraints, but I am wondering if 
> there is no viable workaround. For instance, I don't know the 
> constraints imposed to the optimizer but I would expect some 
> sort of "caching" of values calculated previously when the 
> same node is processed over and over by the same piece of code.
> 
> For instance, say you have a source document like this:
> 
> <top>
>     <a/>
>     <b/>
>     <c/>
>     <d/>
> </top>
> 
> and the output of "b" depends on the position of "a", "c" 
> depends on "b" and so on. When the processor (recursively) 
> processes "d", it should find, somewhere, the value 
> calculated for "c" previously and (magically) save time.
> 
> Now, since I really don't know what kind of optimizing 
> mechanism is in place for the xslt engines I've been using so 
> far (Saxon, Altova, Microsoft), I am asking if you have any 
> idea as how to make recursive algorithms faster in cases like 
> those just described.
> 
> Bye,
> Flavio
> 
> 
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