From f2ce47d96e5704ab4e54666ce75ff3201c8ff84e Mon Sep 17 00:00:00 2001
From: James Hensman <james.hensman@gmail.com>
Date: Tue, 5 Mar 2013 15:58:03 +0000
Subject: [PATCH] Added symmtrical covariance functions

---
 GPy/kern/__init__.py     |  2 +-
 GPy/kern/constructors.py | 10 +++++
 GPy/kern/symmetric.py    | 92 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 103 insertions(+), 1 deletion(-)
 create mode 100644 GPy/kern/symmetric.py

diff --git a/GPy/kern/__init__.py b/GPy/kern/__init__.py
index 008a2e1a..3e20644b 100644
--- a/GPy/kern/__init__.py
+++ b/GPy/kern/__init__.py
@@ -2,5 +2,5 @@
 # Licensed under the BSD 3-clause license (see LICENSE.txt)
 
 
-from constructors import rbf, Matern32, Matern52, exponential, linear, white, bias, finite_dimensional, spline, Brownian, rbf_sympy, sympykern, periodic_exponential, periodic_Matern32, periodic_Matern52, product, product_orthogonal
+from constructors import rbf, Matern32, Matern52, exponential, linear, white, bias, finite_dimensional, spline, Brownian, rbf_sympy, sympykern, periodic_exponential, periodic_Matern32, periodic_Matern52, product, product_orthogonal, symmetric
 from kern import kern
diff --git a/GPy/kern/constructors.py b/GPy/kern/constructors.py
index af82bb24..5d665d93 100644
--- a/GPy/kern/constructors.py
+++ b/GPy/kern/constructors.py
@@ -20,6 +20,7 @@ from periodic_Matern32 import periodic_Matern32 as periodic_Matern32part
 from periodic_Matern52 import periodic_Matern52 as periodic_Matern52part
 from product import product as productpart
 from product_orthogonal import product_orthogonal as product_orthogonalpart
+from symmetric import symmetric as symmetric_part
 #TODO these s=constructors are not as clean as we'd like. Tidy the code up
 #using meta-classes to make the objects construct properly wthout them.
 
@@ -264,3 +265,12 @@ def product_orthogonal(k1,k2):
     """
     part = product_orthogonalpart(k1,k2)
     return kern(k1.D+k2.D, [part])
+
+def symmetric(k):
+    """
+    Construct a symmetrical kernel from an existing kernel
+    """
+    k_ = k.copy()
+    k_.parts = [symmetric_part(p) for p in k.parts]
+    return k_
+
diff --git a/GPy/kern/symmetric.py b/GPy/kern/symmetric.py
new file mode 100644
index 00000000..d493bfb1
--- /dev/null
+++ b/GPy/kern/symmetric.py
@@ -0,0 +1,92 @@
+# Copyright (c) 2012 James Hensman
+# Licensed under the BSD 3-clause license (see LICENSE.txt)
+
+from kernpart import kernpart
+import numpy as np
+
+class symmetric(kernpart):
+    """
+    Symmetrical kernels
+
+    :param k: the kernel to symmetrify
+    :type k: kernpart
+    :param transform: the transform to use in symmetrification (allows symmetry on specified axes)
+    :type transform: A numpy array (D x D) specifiying the transform
+    :rtype: kernpart
+
+    """
+    def __init__(self,k,transform=None):
+        if transform is None:
+            transform = np.eye(k.D)*-1.
+        assert transform.shape == (k.D, k.D)
+        self.transform = transform
+        self.D = k.D
+        self.Nparam = k.Nparam
+        self.name = k.name + '_symm'
+        self.k = k
+        self._set_params(k._get_params())
+
+    def _get_params(self):
+        """return the value of the parameters."""
+        return self.k._get_params()
+
+    def _set_params(self,x):
+        """set the value of the parameters."""
+        self.k._set_params(x)
+
+    def _get_param_names(self):
+        """return parameter names."""
+        return self.k._get_param_names()
+
+    def K(self,X,X2,target):
+        """Compute the covariance matrix between X and X2."""
+        AX = np.dot(X,self.transform)
+        if X2 is None:
+            X2 = X
+            AX2 = AX
+        else:
+            AX2 = np.dot(X2, self.transform)
+        self.k.K(X,X2,target)
+        self.k.K(AX,X2,target)
+        self.k.K(X,AX2,target)
+        self.k.K(AX,AX2,target)
+
+    def dK_dtheta(self,partial,X,X2,target):
+        """derivative of the covariance matrix with respect to the parameters."""
+        AX = np.dot(X,self.transform)
+        if X2 is None:
+            X2 = X
+            ZX2 = AX
+        else:
+            AX2 = np.dot(X2, self.transform)
+        self.k.dK_dtheta(partial,X,X2,target)
+        self.k.dK_dtheta(partial,AX,X2,target)
+        self.k.dK_dtheta(partial,X,AX2,target)
+        self.k.dK_dtheta(partial,AX,AX2,target)
+
+
+    def dK_dX(self,partial,X,X2,target):
+        """derivative of the covariance matrix with respect to X."""
+        AX = np.dot(X,self.transform)
+        if X2 is None:
+            X2 = X
+            ZX2 = AX
+        else:
+            AX2 = np.dot(X2, self.transform)
+        self.k.dK_dX(partial, X, X2, target)
+        self.k.dK_dX(partial, AX, X2, target)
+        self.k.dK_dX(partial, X, AX2, target)
+        self.k.dK_dX(partial, AX ,AX2, target)
+
+    def Kdiag(self,X,target):
+        """Compute the diagonal of the covariance matrix associated to X."""
+        foo = np.zeros((X.shape[0],X.shape[0]))
+        self.K(X,X,foo)
+        target += np.diag(foo)
+
+    def dKdiag_dX(self,partial,X,target):
+        raise NotImplementedError
+
+    def dKdiag_dtheta(self,partial,X,target):
+        """Compute the diagonal of the covariance matrix associated to X."""
+        raise NotImplementedError