Using XSLT 2.0 and FXSL the wanted result is effectively calculated with the 
following one-liner:

    f:zipWith(f:append(),
                    f:scanl1(f:add(), data(/*/*/@X)),
                    f:scanl1(f:add(), data(/*/*/@Y))
                    )


Here is the complete transformation:

<xsl:stylesheet version="2.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 xmlns:f="http://fxsl.sf.net/"
 exclude-result-prefixes="f"
>
  <xsl:import href="../f/func-scanlDVC.xsl"/>
  <xsl:import href="../f/func-Operators.xsl"/>
  <xsl:import href="../f/func-append.xsl"/>
  <xsl:import href="../f/func-zipWith.xsl"/>

  <!-- To be applied on runningTotalsPairwise.xml -->
  <xsl:output omit-xml-declaration="yes" indent="yes"/>

  <xsl:template match="/">
    <xsl:sequence select=
    "f:zipWith(f:append(),
               f:scanl1(f:add(), data(/*/*/@X)),
               f:scanl1(f:add(), data(/*/*/@Y))
               )"/>
  </xsl:template>

</xsl:stylesheet>

When applied on your source xml document :

<DATA>
   <COORD X="10"  Y="10"/>
   <COORD X="5"  Y="-5"/>
   <COORD X="1"  Y="1"/>
 </DATA>

with Saxon 8.2

the wanted result is obtained:

10 10 15 5 16 6


Note also, that this transformation is much more efficient (must be linear) 
than the quadratic time-complexity solutions that are usually offered to 
this kind of problem.

Cheers,
Dimitre Novatchev.



"Alfredo A. Ortega" <ortegaalfredo@g...> wrote in message 
news:e598931c.0501181155.345e38f@p......
> Hi all.
> I'm having this trouble, seems simple but can't make it work:
>
> The data are relative 2D coordinates:
>
> <DATA>
>   <COORD X="10"  Y="10"/>
>   <COORD X="5"  Y="-5"/>
>   <COORD X="1"  Y="1"/>
>   ...
> </DATA>
>
> I need to calculate the intermediate sum of each one, so the output
> for the data will look like:
>
> X=10 Y=10
> X=15 Y=5
> X=16 Y=6
> ...
>
> Now, the data files can have several megabytes, so this:
>
>      <xsl:for-each select="COORD">
> <xsl:value-of 
> select="sum((.|preceding-sibling::COORD)/@X)"/>,<xsl:value-of
> select="sum((.|preceding-sibling::COORD)/@Y)"/>,
>  </xsl:for-each>
>
> is way too slow.
>
> I'm experimenting with recursion with no luck, any help would be very
> much appreciated !
>
> Thanks all for your time -
> Regards, Alfredo Ortega