[Numpy-discussion] help with vectorization
Charles R Harris
Mon Apr 27 15:01:30 CDT 2009
On Mon, Apr 27, 2009 at 1:24 PM, Mathew Yeates <firstname.lastname@example.org> wrote:
> I should add, I'm starting with N rotation angles. So I should rephrase
> and say I'm starting with N angles and N xy pairs.
> Mathew Yeates wrote:
> > I know this must be trivial but I can't seem to get it right
> > I have N 2x2 arrays which perform a rotation. I also have N xy pairs to
> > transpose. What is the simplest way to perform the transformation
> > without looping?
Well, in two dimensions complex multiplication should do the trick.
In : v = array(*4, dtype=complex)
In : a = arange(4)*pi/2
In : around(exp(1j*a)*v,5)
Out: array([ 1.+0.j, 0.+1.j, -1.+0.j, -0.-1.j])
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