[SOSlib-devel] MathML Piecewise function

[Rainer M. <ra...@tb...>]

hi Andrew,

The use of piecewise in the semantic test suite seems to differ from 
official definitions:

E.g. in discontinuityTimeAndDelay-geq-l2.xml
it's:

  <piecewise>
    <piece>
      <apply>
        <geq/>
        <ci> s2 </ci>
        <cn> 4 </cn>
      </apply>
      <cn>1.5</cn>
    </piece>
    <otherwise>
       <cn>0.05</cn>
    </otherwise>
</piecewise>

which is

piecewise(geq(s2, 4), 1.5, 0.05)

in libSBML infix and interpreted as

1.5 if s2 >= 4
and
0.05 otherwise

by SOSlib.
SOSlib produces the results required by the testsuite.


However, at
http://www.w3.org/TR/MathML2/chapter4.html#contm.piecewise
the definition is slightly different:

<piecewise>
   <piece>
       <cn> 0 </cn>
       <apply><lt/><ci> x </ci> <cn> 0 </cn></apply>
   </piece>
   <otherwise>
       <ci> x </ci>
   </otherwise>
</piecewise>

in libSBML infix
piecewise(0, lt(x, 0), x)

interpreted as
0 if x < 0
and x otherwise.

Note, that the if condition of the piece element is BEFORE the 
associated result, while it is AFTER the result in the test suite example.

The same ordering is found in the piecewise example for more pieces - see 
below. The result associated with a piece is always BEFORE the condition.

Am i missing something or is the test suite example (and SOSlib) wrong?

Rainer



The general example with more pieces:

<piecewise>
   <piece>
       <apply><minus/><ci> x </ci></apply>
       <apply><lt/><ci> x </ci> <cn> 0 </cn></apply>
   </piece>
   <piece>
       <cn> 0 </cn>
       <apply><eq/><ci> x </ci> <cn> 0 </cn></apply>
   </piece>
   <piece>
       <ci> x </ci>
       <apply><gt/><ci> x </ci> <cn> 0 </cn></apply>
   </piece>
</piecewise>