This function approximates sqrt(x)*sign(x), such that the derivative is finite and smooth in x=0.
Function Approximation Range
y = sqrtReg(x) y ~= sqrt(abs(x))*sign(x) abs(x) >> delta
y = sqrtReg(x) y ~= x/sqrt(delta) abs(x) << delta

With the default value of delta=0.01, the difference between sqrt(x) and sqrtReg(x) is 16% around x=0.1, 0.25% around x=0.1 and 0.0025% around x=1.


function sqrtReg
  extends Modelica.Icons.Function;
  input Real x;
  input Real delta = 0.01 "Range of significant deviation from sqrt(x)";
  output Real y;
end sqrtReg;


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