#! /usr/bin/env python
#
def annulus_area ( center, r1, r2 ):

#*****************************************************************************80
#
## ANNULUS_AREA computes the area of a circular annulus in 2D.
#
#  Discussion:
#
#    A circular annulus with center (XC,YC), inner radius R1 and
#    outer radius R2, is the set of points (X,Y) so that
#
#      R1^2 <= (X-XC)^2 + (Y-YC)^2 <= R2^2
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    05 July 2018
#
#  Author:
#
#    John Burkardt
#
#  Parameters:
#
#    Input, real CENTER(2), the coordinates of the center.
#    This data is actually not necessary for area calculations.
#
#    Input, real R1, R2, the inner and outer radii of the annulus.
#    0.0 <= R1 <= R2.
#
#    Output, real AREA, the area of the annulus.
#
  import numpy as np
  from sys import exit

  if ( r1 < 0.0 ):
    print ( '' )
    print ( 'ANNULUS_AREA - Fatal error!' )
    print ( '  Inner radius R1 < 0.0.' )
    exit ( 'ANNULUS_AREA - Fatal error!' )

  if ( r2 < r1 ):
    print ( '' )
    print ( 'ANNULUS_AREA - Fatal error!' )
    print ( '  Outer radius R1 < R1 = inner radius.' )
    exit ( 'ANNULUS_AREA - Fatal error!' )

  area = np.pi * ( r2 + r1 ) * ( r2 - r1 )

  return area

def annulus_area_test ( ):

#*****************************************************************************80
#
## ANNULUS_AREA_TEST test ANNULUS_AREA.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    05 July 2018
#
#  Author:
#
#    John Burkardt
#
  import numpy as np
  from r8vec_uniform_01 import r8vec_uniform_01

  print ( '' )
  print ( 'ANNULUS_AREA_TEST' )
  print ( '  ANNULUS_AREA computes the area of an annulus with' )
  print ( '  center = (CX,CY), inner radius R1 and outer radius R2.' )
  
  seed = 123456789

  print ( '' )
  print ( '  (   CX        CY     )    R1         R2         Area' )
  print ( '' )

  center = np.zeros ( 2 )

  for i in range ( 0, 10 ):
    data, seed = r8vec_uniform_01 ( 4, seed )
    center[0] = 10.0 * data[0] - 5.0
    center[1] = 10.0 * data[1] - 5.0
    r1 = data[2]
    r2 = r1 + data[3]
    area = annulus_area ( center, r1, r2 )
    print ( '  (%9.6f,%9.6f)  %9.6f  %9.6f  %9.6f' \
      % ( center[0], center[1], r1, r2, area ) )
#
#  Terminate.
#
  print ( '' )
  print ( 'ANNULUS_AREA_TEST' )
  print ( '  Normal end of execution.' )
  return

if ( __name__ == '__main__' ):
  from timestamp import timestamp
  timestamp ( )
  annulus_area_test ( )
  timestamp ( )