By definition, the partial derivative of this function with respect to x (with a constant) is f(). The complete derivative, however, is dF().
function F extends Modelica.Icons.Function; input Real x "Argument" annotation( Dialog(__Dymola_label = "<html><i>x</i></html>")); input Real a[:] "Coefficients" annotation( Dialog(__Dymola_label = "<html><i>a</i></html>")); input Integer n = 0 "Power associated with the first term (before integral)" annotation( Dialog(__Dymola_label = "<html><i>n</i></html>")); output Real F "Integral" annotation( Dialog(__Dymola_label = "<html><i>F</i></html>")); end F;