# [Numpy-discussion] help with vectorization

Charles R Harris charlesr.harris@gmail....
Mon Apr 27 15:01:30 CDT 2009

```On Mon, Apr 27, 2009 at 1:24 PM, Mathew Yeates <myeates@jpl.nasa.gov> 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 [18]: v = array([1]*4, dtype=complex)

In [19]: a = arange(4)*pi/2

In [20]: around(exp(1j*a)*v,5)
Out[20]: array([ 1.+0.j,  0.+1.j, -1.+0.j, -0.-1.j])

Chuck
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