chg: added polynomial basis func kernel

GPy/kern/src/basis_funcs.py

@@ -102,6 +102,26 @@ class BasisFuncKernel(Kern):
                 phi2 = phi2[:, None]
             return phi1.dot(phi2.T)
 
+class PolinomialBasisFuncKernel(BasisFuncKernel):
+    def __init__(self, input_dim, degree, variance=1., active_dims=None, ARD=True, name='polinomial_basis'):
+        """
+        A linear segment transformation. The segments start at start, \
+        are then linear to stop and constant again. The segments are
+        normalized, so that they have exactly as much mass above
+        as below the origin.
+
+        Start and stop can be tuples or lists of starts and stops.
+        Behaviour of start stop is as np.where(X<start) would do.
+        """
+        self.degree = degree
+        super(PolinomialBasisFuncKernel, self).__init__(input_dim, variance, active_dims, ARD, name)
+
+    @Cache_this(limit=3, ignore_args=())
+    def _phi(self, X):
+        phi = np.empty((X.shape[0], self.degree+1))
+        for i in range(self.degree+1):
+            phi[:, [i]] = X**i
+        return phi
 
 class LinearSlopeBasisFuncKernel(BasisFuncKernel):
     def __init__(self, input_dim, start, stop, variance=1., active_dims=None, ARD=False, name='linear_segment'):