Unless you can make matrices sympifyable, you probably won't be able to use .subs. That isn't to say that you can't write your own specialized function to do the substitution.
There's also some cool stuff you could do here, like implementing a matrix chain multiplication algorithm (http://en.wikipedia.org/wiki/Matrix_chain_multiplication) to compute the most efficient way to multiply a product of matrices ABCD... Aaron Meurer On Mon, Jun 27, 2011 at 9:54 AM, Matthew Rocklin <mrock...@gmail.com> wrote: > Regarding expr.subs(x,matrix): > This is tricky because Matrices aren't sympifiable. I think you would need > to substitute all matrix symbols for matrices at once and then turn the > expression into a Matrix object using the Matrix.__add__ etc methods. Or > maybe any substituted Matrix would become some sort of ImmutableMatrix > object so that it could live inside an Expr. > Regarding other differences: > Being able to substitute computational elements like > Matrices/SparseMatrices/LinearOperators into matrix expressions is > definitely the main motivating application behind symbolic matrices. This is > not my major focus right now though. I'm focusing on turning statistical > statements into computational ones. I've been generating integrals for a > while now and would like to start generating Matrix Expressions like what's > found here. Being able to check the shape of an expression is likely going > to be useful for me. I suspect that there will be more features of matrices > that I'd like exposed other than just that they're not commutative. Knowing > if it is invertible or not is a good example. > Of course, after I generate and simplify these expressions I'll need to > substitute in actual matrices of some form or another, I just haven't gotten > there yet :) > Haven't tried anything yet. > -Matt > > > > > On Mon, Jun 27, 2011 at 10:19 AM, SherjilOzair <sherjiloz...@gmail.com> > wrote: >> Hello Matthew, >> As Aaron says correctly, work on matrices and work on the matrix symbol is >> quite separate. >> The Matrix class provides fundamental operations like addition, >> multiplication. We only have to make Add, Mul call the required routines >> in >> the Matrix class. >> I'm not sure what .flatten does, and my knowledge about the core is only >> minimal. But I think the only time there is a difference between a regular >> symbol and a matrix symbol is when expr.subs(x, matrix) is done. Possibly, >> this could be achieved only by adding some code to the subs function. >> Instead of focussing on things like is_symmetric, is_positive_definite >> (which I agree, are useful), I think making expr.subs(x, matrix) work >> should >> be the first step. x here could be a regular non-commutative Symbol. >> Even if its inelegant, i.e. involves making Add, Mul Matrix-aware, I think >> it would be good if we could try out stuff making .subs work for matrices >> by >> adding code to the present core (.flatten, .subs, etc.). If we succeed, >> then >> more code could be added to get more functionality, even if we don't push >> in >> stuff to the master. Later if this successful, all the Matrix expressions >> code could be ported to a separate MatrixMul, MatrixAdd, etc. Making new >> classes that belong to the core for a small functionality feels like >> overkill right now. >> Have you tried anything out regarding this, Matthew ? >> Regards, >> Sherjil Ozair >> >> -- >> 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/-/uyTjPpzKQhQJ. >> 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. > -- 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.
