r8_sigmoid <- function ( l, b, m, x )

#*****************************************************************************80
#
## r8_sigmoid() evaluates the sigmoid or logistic function.
#
#  Discussion:
#
#    An R8 is a double precision real value.
#
#    The sigmoid function is useful for classification problems in
#    machine learning.  Its value is always between 0 and L.
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    12 September 2026
#
#  Author:
#
#    John Burkardt
#
#  Input:
#
#    real l: the maximum value of the function.  This is often 1.
#
#    real b: the cutoff value, where the function equals l/2.
#    This is often 0.
#
#    real m: the slope, which determines the steepness of the curve
#    and the width of the uncertainty interval.  This is often 1.
#
#    real x: the argument.
#
#  Output:
#
#    real value: the value.
#
{
  value = l / ( 1.0 + exp ( - m * ( x - b ) ) )

  return ( value )
}