On 2 May 2020, at 18:55, Costello, Roger L. costello(_at_)mitre(_dot_)org
<xsl-list-service(_at_)lists(_dot_)mulberrytech(_dot_)com> wrote:
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)
In recent versions of XPath, you can simply do
(1 div (1 + math:exp(-$x)))
(However, it already appears to be mighty accurate -- look at all those
digits to the right of the decimal point)
I hope you don't seriously believe that precision implies accuracy - that
someone who claims the population of the world is 7,345,651,523 is more likely
to be right than someone who says it is 7 billion.
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?
For calculations like this it's best to use xs:double. You don't need any more
precision than this, and exponential/trigonometric functions are likely to be
implemented as double-precision floating point by whatever underlying library
is used.
Michael Kay
Saxonica
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