On Tue, Jul 21, 2009 at 5:35 PM, Doug<mcke...@gmail.com> wrote: > >> Are you aware of the function piecewise(), which seems to do what you >> want? If there is a problem with using it, what is it? > > I wasn't aware of piecewise(), and although it doesn't seem as elegant > or flexible as being able to use Indicator functions in my function > definitions, I think it should work. That said, what I actually want > is to define an additively separable function of two variables where > one component is piecewise. But creating this function with a > piecewise component isn't working. Here's what happens: > > sage: f1(x) = -1 > sage: f2(x) = 2 > sage: f = Piecewise([[(0,pi/2),f1],[(pi/2,pi),f2]]) > sage: f > Piecewise defined function with 2 parts, [[(0, 1/2*pi), x |--> -1], > [(1/2*pi, pi), x |--> 2]] > sage: g(x,y) = y + f(x) > --------------------------------------------------------------------------- > ValueError Traceback (most recent call > last) > > /Users/dmckee/.sage/temp/eve/19724/ > _Users_dmckee_Documents_work_research_mexbeq_sage_spline_numeric_solutions_sage_188.py > in <module>() > > /Applications/sage/local/lib/python2.5/site-packages/sage/functions/ > piecewise.pyc in __call__(self, x0) > 605 if endpts[i] < x0 < endpts[i+1]: > 606 return self.functions()[i](x0) > --> 607 raise ValueError,"Value not defined outside of > domain." > 608 > 609 def which_function(self,x0): > > ValueError: Value not defined outside of domain. > > I must be doing something dumb (again), right?
Piecewise functions of 2 variables are not yet implemented. Sorry. > > Thanks again for all your help! > > Doug > >> >> M. Hampton >> >> On Jul 21, 12:34 pm, Doug <mcke...@gmail.com> wrote: >> >> > I'm trying to do something that seems very simple but isn't working. >> > Hence the post here :) >> >> > I want to define a very simple piecewise linear function. It's linear >> > with slope alpha up to a knot at c and then it's linear with slope >> > beta. Here's what I thought might work: >> >> > f(x) = (x<=c)*alpha*x + (x>c)*(alpha*c + beta*(x-c)) >> >> > Putting the inequalities in there caused a big mess. So I tried >> > defining a Python Indicator function that turns Truth values into 0 or >> > 1, and then I wrapped my relational expressions with it: >> >> > def Indicator(cond): >> > if (cond==True): >> > return 1 >> > else: >> > return 0 >> >> > This didn't work either: >> >> > sage: foo(x) = Indicator(x>4) ; foo >> > x |--> 0 >> >> > Any other ideas? I suppose I could in this case define my piecewise >> > function as a Python function, but then I won't be able to do as much >> > with it later (e.g., differentiate it). >> >> > Thx as usual, Doug > > > --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
