Hi. There's an issue for this too: http://code.google.com/p/sympy/issues/detail?id=2960
Python evaluates "a < b < c" as "(a < b) and (b < c)". Since it's impossible to override the "and" operator, this always returns the first one if it evaluate to True or the second one if it evaluate to True (or False if neither do). Right now, this happens arbitrarily (see http://code.google.com/p/sympy/issues/detail?id=2832). This can be done, however, just not using that syntax. Use the And() object. For example: In [30]: And(10 < x, x < 13) Out[30]: x < 13 ∧ 10 < x In [14]: And(10 < x, x < 13).subs(x, 9) Out[14]: False In [15]: And(10 < x, x < 13).subs(x, 11) Out[15]: True Depending on what you are doing, you might be able to also make use of the Interval() object: In [18]: Interval(10, 13, True, True) Out[18]: (10, 13) We don't have an In() object yet, though (there's an issue for this somewhere, but I couldn't find it, as In is a hard word to search for), so if you want to explicitly represent the fact that some value x is inside an interval, for now, you will have to use And() and inequalities. What you can do is use Interval and it's useful operations (such as union and intersection) until you need an explicit relationship, and then use .as_relational() In [31]: Interval(10, 13, True, True).as_relational(x) Out[31]: x < 13 ∧ 10 < x Of course, whether to use And() and inequalities or intervals depends on what you are doing. Aaron Meurer On Sat, Jan 7, 2012 at 1:53 AM, Kevin Hunter <hunt...@gmail.com> wrote: > Hullo Sympy Group, > > How can I get Sympy to recognize 2+ inequalities in the same expression? In > mathematical optimization it is common to see (and often very convenient to > use) constraint expressions like these: > > 3*x <= 2*y +10 <= 3*z > 10*x >= 15*y >= 20*z >= t > > Which are actually 2 and 3 inequalities. However, when I put those in > directly, it seems only the first or last inequality evaluated is returned: > > ----- > In [1]: ineq1 = 3*x <= 2*y +10 <= 3*z > > In [2]: print ineq1 > 2*y + 10 <= 3*z > > In [3]: ineq2 = 10*x >= 15*y >= 20*z >= t > > In [4]: ineq2 > 15*y <= 10*x > ----- > > Right now, I can create multiple inequalities, but I have to build it via an > inequality per python statement. It would be much more convenient to be > able to do this in one statement. > > Thanks, > > Kevin > > P.S. Sympy is already proving to be a boon to my project, spotting some > bugs and inconsistencies in my logic. Thanks! > > -- > You received this message because you are subscribed to the Google Groups > "sympy" group. > To view this discussion on the web visit > https://groups.google.com/d/msg/sympy/-/_BmcIHE29zcJ. > To post to this group, send email to sympy@googlegroups.com. > To unsubscribe from this group, send email to > sympy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sympy?hl=en. -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com. To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
