def grad_coef(self, x, beta=None, gamma=None):
"""
See Interp2D.grad_coef.
This is the variable gamma version.
"""
if beta is None:
beta = self.beta
if gamma is None:
gamma = exp(self.log_gamma_interp.interp(x))
return Interp2D.grad_coef(self, x, beta, gamma)
