Applies secondary depth constraint to each population

        See :func:`EclipsePopulation.apply_secthresh`;
        all arguments passed to that function for each population.

def apply_secthresh(self, secthresh, **kwargs):
        """Applies secondary depth constraint to each population

        See :func:`EclipsePopulation.apply_secthresh`;
        all arguments passed to that function for each population.

        """

        if 'secondary depth' not in self.constraints:
            self.constraints.append('secondary depth')
        for pop in self.poplist:
            if not isinstance(pop, EclipsePopulation_Px2):
                pop.apply_secthresh(secthresh, **kwargs)
        self.secthresh = secthresh