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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _density_par(self,dangle,tdisrupt=None):
 """The raw density as a function of parallel angle"""

        if tdisrupt is None: tdisrupt= self._tdisrupt
        dOmin= dangle/tdisrupt
        # Normalize to 1 close to progenitor
        return 0.5\
            *(1.+special.erf((self._meandO-dOmin)\
                                 /numpy.sqrt(2.*self._sortedSigOEig[2])))