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September 12, 2000 17:18Subject:

Re: RFC 81 and broadcastingMessage ID:

000f01c01d18$3945cbf0$d5252ccb@optimaldecisions.comChristian Soeller wrote: > Maybe that's already implicit in the broadcasting proposal but it > wouldn't hurt to spell it out: > > A dimension size of 1 should be broadcasted to match that of the > other operand. So, for example, the following shapes (returned by > @#array) are compatible: > > @c = @a * @b > > result shape shape @a shape @b > > [4,8,5] [4,1,5] [4,8,5] > [5,3,2] [1,3,2] [5,1,2] > Isn't that already spelt out? <quote> If the operands are a column vector and a row vector, the elements of each vector are combined into a two dimensional array: my int @vec1 = (2,3); # 1st dimension my int @vec2 = ([2],[3]); # 2nd dimension @i = @vec1*@vec2; # ([2*2,3*2],[2*3,3*3]) == ([4,6],[6,9]) Equivalent combinatorial broadcasting occurs if the operands are perpendicular planes (creating a cube), and so forth for higher dimensional arrays. </quote> > In that respect it would be nice to have a slicing syntax to introduce > 'dummy' dimensions of size 1 (e.g. Yorick uses the concept of a > pseudo-index, [1]; similarly NumPy [2]; PDL has dummy dimensions via '*' > using C<slice>): > > @a = sin @x; # 1D array > @b = cos @x; > > @twod = @a * @b[-;]; > > which would be the same as > > @twod[|i;|j] = @a[|i] * @b[|j]; > So is your proposal basically that we need a way to transpose arrays easily? To be honest, I don't really get the point of stuff like NumPy's "NewAxis", so I might be misunderstanding your proposal. But at least for your example, we would just have: @a = sin @x; # 1D array @b = cos @x; @twod = @a * transpose(@b); or if we don't have a transpose() builtin: @twod = @a * part(1, @b);Thread Previous | Thread Next

- RFC 81 and broadcasting by Christian Soeller
**Re: RFC 81 and broadcasting**by Jeremy Howard- Re: RFC 81 and broadcasting by Christian Soeller

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