RE: Unexpected result in sum

 Subject: RE: Unexpected result in sum From: "Michael Kay" Date: Sat, 10 Nov 2007 00:01:11 -0000
```> Why does this not output 0.00?  When formatted, I end up with -\$0.00.

The sum is not zero because of the rounding errors that occur with floating
point arithmetic. When values such as -1.11 are converted to binary floating
point, a small rounding error occurs. You can avoid this (if it's
significant) by using decimal arithmetic rather than floating point.
Alternatively, you can round off to two decimal places after doing the
summation.

There's a legitimate question about whether format-number() when applied to
a very small negative number should output 0.00 or -0.00. I assume that's
how you are doing the formatting. Saxon is doing what the spec says it
should do, but it seems less than ideal.

This is nothing to do with negative zero, by the way. The total is not
negative zero, but a small non-zero negative number, and the rules for
format-number say that a minus sign is used when the supplied value is
negative, even if the value after rounding is zero.

Michael Kay
http://www.saxonica.com/

>
> I've read what I can find on negative zero, but can't see how
> this node set and operation could produce it.
>
> Using Saxon 8.9 processor (internal to Oxygen.)
>
> Input:
> <?xml version="1.0" encoding="UTF-8"?>
> <a>
>     <b>1103.86</b>
>     <b>1829.30</b>
>     <b>-853.77</b>
>     <b>-243.17</b>
>     <b>-1.11</b>
>     <b>-1296.66</b>
>     <b>588.52</b>
>     <b>849.25</b>
>     <b>-1976.22</b>
> </a>
>
> Output:
> <?xml version="1.0" encoding="UTF-8"?>
> <a>
>    <sum-b>-2.2737367544323206E-13</sum-b>
>    <sum-nodes>-2.2737367544323206E-13</sum-nodes>
> </a>
>
> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
> version="2.0">
>     <xsl:output method="xml" indent="yes"/>
>
>     <xsl:template match="/a">
>         <a>
>             <sum-b>
>                 <xsl:value-of select="sum(b)"/>
>             </sum-b>
>
>             <xsl:variable name="nodes" select="b"/>
>
>             <sum-nodes>
>                 <xsl:value-of select="sum(\$nodes)"/>
>             </sum-nodes>
>         </a>
>     </xsl:template>
> </xsl:stylesheet>
>
> Thanks!
> Angela Williams
> Office: 512.344.1547 ~ Fax: 512.397.6656
> Angela.Williams@xxxxxxxxxxxxxxxxxx

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