Re: [xsl] Is this the best way to compute a sigmoid function?

["Martin Honnen martin.honnen@xxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

On 02.05.2020 19:55, Costello, Roger L. costello@xxxxxxxxx wrote:
> Hi Folks,
>
> I have a variable $x that has a value such as 0.6
>
> I want to compute the result of evaluating this sigmoid function:
>
>       1
> ----------------
> (1 + e**-x)
>
> That is, compute 1 divided by (1 + e raised to the -x power)

Does your environment not support
https://www.w3.org/TR/xpath-functions/#func-math-exp?

> I am using the exp template in Dimitre's FXSL library.
>
> [Dimitre, incredible library]
>
> I created a wrapper function that simply calls Dimitre's exp template:
>
> <xsl:function name="f:e" as="xs:decimal">
>      <xsl:param name="x" as="xs:decimal" />
>
>      <xsl:call-template name="exp">
>          <xsl:with-param name="pX" select="$x" />
>      </xsl:call-template>
> </xsl:function>
>
> Then I computed the sigmoid function this way:
>
> <xsl:variable name="e-to-the-minus-x-power" select="f:e(-$x)"
as="xs:decimal" />
> <xsl:value-of select="1 div (1 + $e-to-the-minus-x-power)"/>
>
> When $x has the value 0.6 I get this result: 0.645656306189717285
>
> Do you see any errors in how I am computing the sigmoid function?
>
> Is there a better way to do it? That is, one that returns more accurate
results? (However, it already appears to be mighty accurate -- look at all
those digits to the right of the decimal point) Notice that for the variable
$e-to-the-minus-x-power I specified it this way: as="xs:decimal". Should I
have specified it this way: as="xs:float" instead? Would that yield
better/more-accurate/more-reliable/more-whatever results?
> Any suggestions you might have would be greatly appreciated.
>
> /Roger