def xs(self, x0):
'''(INTERNAL) Eta summation (C{float}).
'''
return fdot3(self._ab, self._cy, self._shx, start=x0)
def ps(self, p0):
'''(INTERNAL) P summation (C{float}).
'''
return fdot3(self._pq, self._cy, self._chx, start=p0)
def qs(self, q0):
'''(INTERNAL) Q summation (C{float}).
'''
return fdot3(self._pq, self._sy, self._shx, start=q0)
def ys(self, y0):
'''(INTERNAL) Ksi summation (C{float}).
'''
return fdot3(self._ab, self._sy, self._chx, start=y0)