Thats the expected output since 1 is not in the domain:
sage: f.domain()
(0, 1) + (1, 3) + (3, 4)
You probably want
sage: g = piecewise([[(0,1),x], [[1,3],2-x], [(3,4),x-4]])
sage: g.domain()
(0, 4)
sage: g.plot([0,4])
On Sunday, May 22, 2016 at 12:06:27 AM UTC+2, paulmasson wrote:
>
> Since the SageMathCell server has been updated to Sage 7.2, I've been
> experiencing issues with piecewise functions. For example, define a simple
> saw tooth with
>
> f=piecewise([[(0,1),x],[(1,3),2-x],[(3,4),x-4]])
>
> The endpoints appear to be defined just fine,
>
> f.end_points()
>
> [0, 1, 3, 4]
>
>
> but if I evaluate f(1) I get this message:
>
>
> ---------------------------------------------------------------------------
> ValueError Traceback (most recent call last)
> <ipython-input-1-3e93894c0576> in <module>()
> 2 #show(plot(f))
> 3 f.end_points()
> ----> 4 f(Integer(1))
>
> /home/sc_serv/sage/local/lib/python2.7/site-packages/sage/symbolic/function_factory.pyc
> in new_f(ex, *args, **kwds)
> 400 new_args = list(ex._unpack_operands())
> 401 new_args.extend(args)
> --> 402 return f(ex, *new_args, **kwds)
> 403 return new_f
>
> /home/sc_serv/sage/local/lib/python2.7/site-packages/sage/functions/piecewise.py
> in __call__(cls, self, parameters, variable, value, **kwds)
> 447 if value is not None:
> 448 substitution[variable] = value
> --> 449 return self.subs(substitution)
> 450
> 451 def _fast_float_(cls, self, *args):
>
> /home/sc_serv/sage/src/sage/symbolic/expression.pyx in
> sage.symbolic.expression.Expression.substitute
> (/home/sc_serv/sage/src/build/cythonized/sage/symbolic/expression.cpp:27845)()
> 4883
> 4884 return new_Expression_from_GEx(self._parent,
> -> 4885 self._gobj.subs_map(smap, 0))
> 4886
> 4887 subs = substitute
>
> /home/sc_serv/sage/local/lib/python2.7/site-packages/sage/functions/piecewise.py
> in _subs_(self, subs_map, options, parameters, x)
> 228 if domain.contains(point):
> 229 return subs_map.apply_to(func, 0)
> --> 230 raise ValueError('point {} is not in the
> domain'.format(point))
> 231
> 232 @staticmethod
>
> ValueError: point 1 is not in the domain
>
>
> Adding decimal points to the endpoints to coerce them to float values
> doesn't fix the problem.
>
> Sage 7.2 includes http://trac.sagemath.org/ticket/14801 that is supposed
> to fix problems with symbolics. Am I missing some new behavior or is this a
> bug?
>
>
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