[Numpy-discussion] adding a .M attribute to the array.
oliphant at ee.byu.edu
Wed Mar 6 13:06:50 CST 2002
> > Other suggestions?
> Here is one suggestion that is based on the observation that all we need
> is an easy way to tell that the following operation should be applied
> as a matrix operation. So, the suggestion is to provide an attribute or a
> member function that returns an array (note, not a Matrix instance) that
> has a bit, called it asmatrix, set true but _only_ temporally. The bit is
> cleaned on every operation. And before applying an operation, the
> corresponding method (currently there seem to be only four relevant
> methods: __mul__, __pow__ and their r-versions) checks if either of
> the operants has asmatrix bit true, then performs the corresponding matrix
> operation, otherwise the default element-wise operation. And before
> returning, it cleans up asmatrix bit.
Frankly, I like this kind of proposal. I disagree with Konrad about the
separation between arrays and matrices. From my discussions with other
people, it sounds like this is actually a point of disagreement for many
in the broader community.
To me, matrices are just arrays of rank <=2 which should be interpreted
with their specific algebra.
> For the sake of an example, let .m be Numeric array attribute that when
> accessed sets asmatrix=1 and returns the array.
> a * b - is element-wise multiplication
> a.m * b, a * b.m - are matrix multiplications, the resulting
> array, as well a and b, have asmatrix=0
> a.m ** -1 - is matrix inverse
> sin(a) - element-wise sin
> sin(a.m) - matrix sin
> To summarize the main ideas:
> * array has asmatrix bit that most of the time is false.
> * there is a way to set the asmatrix bit true, either by .m or .M
> attributes or .m(), .M(), .. methods that return the same array.
> * __mul__, __pow__, etc. methods check if either operant has asmatrix
> true, then performs the corresponding matrix operation, otherwise
> the corresponding element-wise operation.
> * all operations clean asmatrix bit.
Again, I wouldn't mind it, but I suspect the more aesthetically critical
on the list will dislike it because it blurs the (currently clumsy)
distinction between arrays and Matrices that I'm beginning to see people
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