This information is part of the Modelica Standard Library maintained by the Modelica Association.

This function is used to approximate the equation

y = if x > 0 then y1 else y2;

by a smooth characteristic, so that the expression is continuous and differentiable:

y = smooth(1, if x >  x_small then y1 else
              if x < -x_small then y2 else f(y1, y2));

In the region -x_small < x < x_small a 2nd order polynomial is used for a smooth transition from y1 to y2.

y = regStep(x, y1, y2, x_small)

x	Type: Real Description: Abscissa value
y1	Type: Real Description: Ordinate value for x > 0
y2	Type: Real Description: Ordinate value for x < 0
x_small	Default Value: 1e-5 Type: Real Description: Approximation of step for -x_small <= x <= x_small; x_small >= 0 required

y	Type: Real Description: Ordinate value to approximate y = if x > 0 then y1 else y2