#! /usr/bin/env python3
#
def gradient_example ( ):

  from sympy import cos
  from sympy import exp
  from sympy import pprint
  from sympy import symbols
  from sympy.vector import CoordSys3D
  from sympy.vector import gradient
  import sympy

  print ( '' )
  print ( 'gradient_example():' )
  print ( '  sympy version: ' + sympy.__version__ )
  print ( '  Compute the gradient vector of a scalar field f(x,y,z).' )
  print ( '  f(x,y,z) = 3 exp(-x^2) + 7x^2/y + 5 cos(y) + 10z.' )
#
#  Define a coordinate system.
#
  C = CoordSys3D ( 'C' )
#
#  Name the components of the coordinate system.
#
  x, y, z = C.x, C.y, C.z
#
#  Define the scalar field.
#
  fxyz = 3 * exp ( - x**2 ) + 7 * x**2 / y + 5 * cos ( y ) + 10 * z
#
#  Compute the gradient.
#
  grad = gradient ( fxyz )
  pprint ( grad )

  return

if ( __name__ == "__main__" ):
  gradient_example ( )