features.py 文件源码

def hessian(self, x, d=None):
        """
        Computes Hessian matrix
        """
        d = calc_distances(x) if d is None else d
        if d.ndim == 1: d = squareform(d)

        H = np.zeros((3*len(x), 3*len(x)))
        n = self.n

        for i in range(len(x)):
            for j in range(len(x)):

                if j == i: continue

                dx = x[i]-x[j]
                r  = d[i,j]
                h  = n / r**(0.5*n+2) * ((n+2) * np.multiply.outer(dx,dx) - np.eye(3) * r)

                H[3*i:3*(i+1), 3*j:3*(j+1)]  = -h 
                H[3*i:3*(i+1), 3*i:3*(i+1)] +=  h

        return H