Dear All,
I'm working on a piece of optimisation code where it turns out to be
mathematically convenient to have a matrix where a few pre-chosen elements must
be computed at evaluation time for the dot product (i.e. matrix multiplication)
of a matrix with a vector.
As I see the problem, there are two basic approaches to accomplishing this.
First (and perhaps conceptually simplest, not to mention apparently faster)
might be to stash appropriate functions at their corresponding locations in the
matrix (with the rest of the matrix being constants, as usual). I mucked around
with this for a little while in iPython, and it appears that having dtype ==
object_ works for stashing the references to the functions, but fails to allow
me to actually evaluate the function(s) when the matrix is used in the dot
product.
Does anyone have any experience with making such a beast work within numpy? If
so, how?
The second basic approach is to build a ufunc that implements the switching
logic, and returns the constants and evaluated functions in the appropriate
locations. This seems to be the more do-able approach, but it requires the
ufunc to be aware of both the position of each element (via index, or somesuch)
as well as the arguments to the functions themselves being evaluated at the
matrix elements. It appears that frompyfunc() nearly does what I want, but I am
currently failing to see how to actually *use* it for anything more elaborate
than the octal example code (i.e. one value in, and one value out). Does anyone
have any other more elaborate examples they can point me towards?
Thanks in advance for any help you might be able to provide!
Frank Horowitz
fr...@horow.net
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