[Matrix-SIG] matrix transformations on vector graphics

[Warren Focke]

On Wed, 15 Apr 1998, David Ascher wrote:

> On Wed, 15 Apr 1998, Just van Rossum wrote:
> > 
> > Is there a convenient way to apply the matrix to the vector array?
> 
...
> And then, you can just use the 'dot()' function:
> 
> 	>>> Numeric.dot(v, tm)
> 	array([[   0.,    0.],
> 	       [  10.,    0.],
> 	       [ 100.,  -75.]])
> 
...
> > If I turn the x and y values into separate arrays, I could probably do
> > something like this:
> >
> > [x, y] = Numeric.transpose(v)
> > xnew = tm[0][0] * x + tm[0][1] * y + tm[2][0]
> > ynew = tm[1][0] * x + tm[1][1] * y + tm[2][1]
> >
> > But if I in general would prefer xy pairs, I would have to do
> > Numeric.transpose() before and after I do this. Or is transpose()
> > relatively cheap? Did I just answer my own question?
> 
> transpose is very cheap, since it doesn't move any of the data, just the
> description of the data.
> 

But PyArray_ContiguousFromObject eventually gets called on both arguments
to Numeric.dot.  Does this not copy the data of transposed arrays,
negating the ``cheapness'' in this case (on the input side, at least)?

Warren Focke