f4 <- function ( x )

#*****************************************************************************80
#
## f4() evaluates a nonlinear system of 4 equations.
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    09 April 2021
#
#  Author:
#
#    John Burkardt
#
#  Input:
#
#    double X[N], the variable values.
#
#  Output:
#
#    double FX[N], the function values.
#
{
  n <- length ( x )

  fx <- c ( 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 )

  for ( i in 1 : n )
  {
    fx[i] = ( 3.0 - 2.0 * x[i] ) * x[i] + 1.0

    if ( 1 < i )
    {
      fx[i] = fx[i] - x[i-1]
    }

    if ( i < n )
    {
      fx[i] = fx[i] - 2.0 * x[i+1]
    }
  }

  return ( fx )
}