.ModelicaTest.Fluid.TestUtilities.TestRegRootDerivative .ModelicaTest.Fluid.TestUtilities.TestRegRootDerivativeThis test model demonstrates that the regRoot(..) function cannot be differentiated, if multiplied with a discontinuous factor as it is usual for pressure drop components where upstream properties are used. In such a case, the regRoot2(..) function should be used. In order to test this behaviour, change the line "yd=0" to "yd = der(y)".