This information is part of the Modelica Standard Library maintained by the Modelica Association.
Indicate smoothness of expression
If p>=0 smooth(p, expr) returns expr and states that expr is p times continuously differentiable, i.e.: expr is continuous in all real variables appearing in the expression and all partial derivatives with respect to all appearing real variables exist and are continuous up to order p.
The only allowed types for expr in smooth are: real expressions, arrays of allowed expressions, and records containing only components of allowed expressions.
The noEvent operator implies that real elementary expressions are taken literally instead of generating crossing functions. The smooth operator should be used instead of noEvent, in order to avoid events for efficiency reasons. A tool is free to not generate events for expressions inside smooth. However, smooth does not guarantee that no events will be generated, and thus it can be necessary to use noEvent inside smooth. [Note that smooth does not guarantee a smooth output if any of the occurring variables change discontinuously.]
Real x, y, z; equation x = if time<1 then 2 else time-2; z = smooth(0, if time<0 then 0 else time); y = smooth(1, noEvent(if x<0 then 0 else sqrt(x)*x)); // noEvent is necessary.