> It's highly unlikely you'd create an Indexed that did an operation with a > Matrix, but a Matrix with Indexed elements, yes as this is what would > happen in a finite difference model. >
Would you write it as Matrix([indexed_thing, indexed_thing_2, ...]), or just use the indexed object support for the outer Matrix as is already shown in the docs? On Mon, Aug 4, 2014 at 11:34 PM, Tim Lahey <tim.la...@gmail.com> wrote: > > > On 5 Aug 2014, at 0:14, James Crist wrote: > > @Tim: >> >> They're for representing tensors. Of course, the can be used for a number >> >>> of things, including calculating finite difference formulas. In my case, >>> tensors are useful for stress analysis, especially in changing reference >>> frames. Other uses I know about relate to various physics topics. >>> >>> >> Oh neat! I took a class on finite elements, but we never referred to them >> as tensors. I'll have to look into that. >> > > Not really, finite differences are a different approach to solving PDEs. > With finite differences you have nodes at i-1, i, and i+1 (and possibly in > time or in multiple dimensions). You approximate the derivative with > differences in the values at those points. You can use Indexed to represent > these. As the mesh gets more fine, it's a closer representation of the > derivative as the formulas come from Taylor series. I guess you could think > of them as tensors, but it's not a common thing. It's just that Indexed > provides a useful way you can do the representation. > > The tensors are from continuum mechanics. The more sophisticated analysis > of material deformation all comes down to this, and tensors are the usual > way to represent things. > > > >> Have you used code generation with them? If you have and have some example >> code with them you could send my way that'd be great. It'd be really >> useful >> for me to understand exactly what the scope of support for them is, as I >> work around the implementation trying to get other things to work. >> >> > No, I haven't. Sorry. > > > For example, would you ever create an Indexed that did an operation with a >> Matrix? Or a Matrix with Indexed's as elements? What I'm trying to see is >> if there is any reason for them ever to coexist, or can the >> implementations >> assume that they're never used together? The tensor code makes everything >> really complicated as the loops introduce a scope of sorts (symbol y[i] >> isn't the same value at each point in a loop). >> > > It's highly unlikely you'd create an Indexed that did an operation with a > Matrix, but a Matrix with Indexed elements, yes as this is what would > happen in a finite difference model. > > Cheers, > > Tim. > > > -- > You received this message because you are subscribed to a topic in the > Google Groups "sympy" group. > To unsubscribe from this topic, visit https://groups.google.com/d/ > topic/sympy/zRytRaEH5R8/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > sympy+unsubscr...@googlegroups.com. > To post to this group, send email to sympy@googlegroups.com. > Visit this group at http://groups.google.com/group/sympy. > To view this discussion on the web visit https://groups.google.com/d/ > msgid/sympy/B68EFEFD-3CCC-4D2F-93F9-A326BE280EA1%40gmail.com. > > 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 http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CAJ2L7mdSk_RSWJ9FvU3iERO9c%3DWTP7y3ZaENFpJZXGdn3s5U7w%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
