rotate rotation of a set of points

## Syntax

    xy1=rotate(xy,[theta,orig])

## Arguments

xy

  matrix of size (2,.).

xy1

  matrix of size (2,.).

theta

  real, angle in radians; default value is 0.

orig

  center of the rotation [xc;yc]; default value is [0;0].

## Description

`rotate` performs a rotation with angle `theta`:

`xy1(:,i) = M(theta) *(xy(:,i) - orig) + orig`

where `M` stands for the corresponding rotation matrix.

## Examples

    xsetech([0,0,1,1],[-1,-1,1,1])
    xy=[(0:0.1:10);sin(0:0.1:10)]/10;
    for i=2*%pi*(0:10)/10,
      [xy1]=rotate(xy,i);
      xpoly(xy1(1,:),xy1(2,:),"lines")
    end

xsetech([0,0,1,1],[-1,-1,1,1]) xy=[(0:0.1:10);sin(0:0.1:10)]/10; for i=2*%pi*(0:10)/10, [xy1]=rotate(xy,i); xpoly(xy1(1,:),xy1(2,:),"lines") end