Le jeudi 10 novembre 2011 à 20:27 +0530, gsagrawal a écrit : > i mentioned that sorting of args will not work here. > Consider below example, > k1=Add([x+y,-z],evaluate=False) > k2=Add([x-z,y],evaluate=False) > > > in this case k1.args are (x+y,-z) and k2.args are (x-z,y) . > So sorting here will not improve the result. > also if i use flatten method of this class than it sums up the common > terms(against the evaluate=False) > > > Is there any way to bypass this issue ?
Don't use evaluate=False. This feature is a hack, it does not and cannot work properly. Besides, using 'evaluate=False' means that you only consider the arguments of an operation, but not its result. However, k1 and k2 are equal only if you consider the result of the operations, while their arguments are completely different. > On Thu, Nov 10, 2011 at 8:16 PM, Chris Smith <[email protected]> wrote: > On Thu, Nov 10, 2011 at 6:45 PM, gsagrawal > <[email protected]> wrote: > > Hi, > > In my project i have to use evaluate=false at the time when > i am creating > > any Add or Mul Class object.In this case i am facing the > problem when i > > apply equality check on these object. this issue is because > of ordering of > > arguments. > > Please consider below example > > > k2=Mul(*[x,y,2],evaluate=False) > > > k1=Mul(*[x,2,y],evaluate=False) > > >print k1==k2 > > result in false > > as k2.args are (x,y,2) and k1.args are (x,2,y) > > so while comparison as it checks for tuple equality it > returns false . > > Is there any way i can get the wanted result ? > > Also ,if i put some operation on tuples (like reversed the > order and than > > check ) it fails in the cases when k1 and k2 are formed from > different Mul > > Objects (like when k1.args = 2*x,y and k2.args=2*y,x) > > Please suggest some way > > Thanks > > > Issue 2805 identifies this as a potential change to sympy. In > the mean > time, for your own equality testing purposes, consider > hash-sorting > your args: > > >>> args = [x,y,2] # must be a list to use sort method > >>> args.sort(key=hash) > >>> Mul(*args, evaluate=False) > 2*x*y > >>> _.args > (2, y, x) > > -- > You received this message because you are subscribed to the > Google Groups "sympy" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to sympy > [email protected]. > 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 [email protected]. > To unsubscribe from this group, send email to sympy > [email protected]. > 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 [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
