@memoize()<EOL><INDENT>def _skew(self, x, z, d=<NUM_LIT:0>):<DEDENT>
<EOL>kval = (np.tanh(self._poly(z, self._kurtosis_coeffs(d)))+<NUM_LIT:1>)/<NUM_LIT><EOL>bdpoly = np.array([<EOL>-<NUM_LIT>,  <NUM_LIT>, -<NUM_LIT>,<EOL>-<NUM_LIT>, <NUM_LIT>, <NUM_LIT><EOL>])<EOL>top = np.polyval(bdpoly, kval)<EOL>skew = self._poly(z, self._skew_coeffs(d))<EOL>skewval = top*(np.tanh(skew) + <NUM_LIT:1>) - top<EOL>return skewval*(<NUM_LIT:3>*x - x**<NUM_LIT:3>)<EOL>
returns the kurtosis parameter for direction d, d=0 is rho, d=1 is z