2014-12-04 9:32 UTC+01:00, David Roe <roed.m...@gmail.com>:
>> abs(matrix) is currently returning the determinant (and this goes back
>> to the early implementation in 2006!). If anybody contests the fact
>> that it should return the matrix whose entries are the absolute value
>> of the initial matrix, please tell me.
>
> I don't think that it should be the matrix consisting of absolute
> values of entries, since that only works for matrices over a ring with
> an absolute value. Using
> it as a determinant is consistent with standard notation, though I
> agree that we don't usually say absolute value in this context.
abs(m) is not a standard notation for the determinant... (though |m|
is as Simon mentioned). My conclusion is that we should just forbid
__abs__ for matrices.
> In general, I'm opposed to matrix operations which do the same thing
> to each entry, unless we're very explicit about it. I would prefer a
> method 'elementwise()' which takes in a method (either the global
> function abs or the string 'abs') and applies it to each entry.
All right, I can do that in the ticket. It is perfectly fine to send a
function to .elementwise() because it can be optimized for abs as it
is the one from __builtin__.
def elementwise(self, f):
if f is abs:
# try to find optimized routine
try:
self._elementwise_abs()
except AttributeError:
pass
# default behavior
return self.parent()([[f(x) for x in row] for row in self.rows()])
It would be nice to guarantee uniqueness of other functions like
cos,sin,exp, ... to get optimized subroutines for matrices over
various real and complex numbers.
Vincent
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