On Sun, 27 Jul 2008 02:23:11 am [EMAIL PROTECTED] wrote: > How about just making a matrix multiply function that can take many > arguments? I think this is pretty readable: > > mmul(a, b, c, d) > > Additionally, mmul could then optimize the order of the > multiplications (e.g., depending the dimensions of the matrices, it > may be much more efficient to perform a*((b*c)*d) rather than > ((a*b)*c)*d).
But be careful there: matrix multiplication is associative, so that a*b*c = (a*b)*c = a*(b*c), but that doesn't necessarily apply once the elements of the matrices are floats. For instance, a*(b*c) might underflow some elements to zero, while multiplying (a*b)*c does not. As a general rule, compilers should not mess with the order of floating point calculations. Also, some classes that people might want to multiply may not be associative even in principle. E.g. the vector cross product: (a*b)*c != a*(b*c) in general. I think a product() function that multiplies the arguments from left to right would be useful. But it won't solve the problems that people want custom operators to solve. I'm not even sure if it will solve the problem of matrix multiplication. -- Steven. _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
