def f2(x,returntype=LINALGMAXFLOAT):
'''
Second derivative of sigmoid
(q - p) p q
'''
x = np.float128(x)
logp = -np.logaddexp(ZERO128,-x)
logq = -np.logaddexp(ZERO128, x)
p = np.exp(np.minimum(F128EMAX,logp))
q = np.exp(np.minimum(F128EMAX,logq))
return returntype((q-p)*q*p);
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