I am not familiar with this trick, but just because engineers in some area hack together some method that is mathematically dubious, doesn't mean it should be introduced as a default in sympy. (Maybe it should, maybe it is harmless?) An example that also involves context that sympy would not know about is how to deal with certain expressions involving infinity. E.g. is 0*oo equal to 0 or "indeterminate" ? what about oo = oo ?
One way of looking at this may be to build some "mechanics" toolkit with such tricks. RJF On Sunday, August 14, 2016 at 3:12:29 AM UTC-7, SAMPAD SAHA wrote: > > > In Mechanics, while solving beam bending problems, we need to find out the > reaction force at first. There is a trick I have learned from Jason. > Suppose there is beam of length l, then we at first find the load > distribution using variables multiplied by dirac deltas in place of > reaction forces. After finding shear force curve and bending moment curve > in terms of those variables, we equates them to 0 for x = l+ > > Now for tthis case we have to use the limit. > > Regards > Sampad Kumar Saha > Mathematics and Computing > I.I.T. Kharagpur > > On Sun, Aug 14, 2016 at 12:27 PM, Aaron Meurer <asme...@gmail.com > <javascript:>> wrote: > >> I agree that DiracDelta doesn't make sense except under an integral sign. >> But as a function that is 0 everywhere except for one point, in a limit, it >> can be replaced with 0, which is what SymPy's limit() appears to be doing. >> I am curious how you are ending up with an expression with a DiracDelta >> that you need to take a limit of, though. >> >> Aaron Meurer >> >> On Sat, Aug 13, 2016 at 8:34 PM, Richard Fateman <fat...@gmail.com >> <javascript:>> wrote: >> >>> Since DiracDelta is a distribution, not a function, and presumably the >>> limit program is oriented toward finding limits of analytic functions, >>> it would be fairly reasonable for the limit program to not work on >>> this kind of expression. The mathematical context in which DiracDelta is >>> understood and useful is under an integral sign. >>> >>> I have not tried sympy on this example, but it seems to me >>> that expecting sympy to answer a poorly formulated question >>> "correctly" is not going to reveal a bug in the program. It >>> is "user error". >>> >>> RJF >>> >>> >>> On Saturday, August 13, 2016 at 5:25:22 AM UTC-7, SAMPAD SAHA wrote: >>>> >>>> Suppose I want to find the value of f(x) for >>>> f(x) = DiracDelta(x - 30) + Heaviside(x) at x = 30+ in sympy. How can >>>> we do this? >>>> >>>> Regards >>>> Sampad Kumar Saha >>>> Mathematics and Computing >>>> I.I.T. Kharagpur >>>> >>>> >>>> >>>> >> -- >> You received this message because you are subscribed to the Google Groups >> "sympy" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to sympy+un...@googlegroups.com <javascript:>. >> To post to this group, send email to sy...@googlegroups.com <javascript:> >> . >> Visit this group at https://groups.google.com/group/sympy. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/sympy/CAKgW%3D6JAO7i1f-X6uw-WiiztsV%3DXh2Tt74crv3ULhFKr1oz2Bg%40mail.gmail.com >> >> <https://groups.google.com/d/msgid/sympy/CAKgW%3D6JAO7i1f-X6uw-WiiztsV%3DXh2Tt74crv3ULhFKr1oz2Bg%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> For more options, visit https://groups.google.com/d/optout. >> > > -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sympy+unsubscr...@googlegroups.com. To post to this group, send email to sympy@googlegroups.com. Visit this group at https://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/1ca3f3e9-4f9b-4cea-bdcb-5d62f3e8ee44%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
