diff --git a/GPy/core/parameterised.py b/GPy/core/parameterised.py
index 007f1b25..b5d880a3 100644
--- a/GPy/core/parameterised.py
+++ b/GPy/core/parameterised.py
@@ -56,7 +56,7 @@ class parameterised(object):
         return copy.deepcopy(self)
 
 
-    def tie_param(self, which):
+    def tie_params(self, which):
         matches = self.grep_param_names(which)
         assert matches.size > 0, "need at least something to tie together"
         if len(self.tied_indices):
diff --git a/GPy/examples/classification.py b/GPy/examples/classification.py
index 00842e3b..c6b7f0ac 100644
--- a/GPy/examples/classification.py
+++ b/GPy/examples/classification.py
@@ -62,7 +62,7 @@ def oil():
 
     # Contrain all parameters to be positive
     m.constrain_positive('')
-    m.tie_param('lengthscale')
+    m.tie_params('lengthscale')
     m.update_likelihood_approximation()
 
     # Optimize
diff --git a/GPy/examples/tutorials.py b/GPy/examples/tutorials.py
index 9d892b8e..2bc9ba60 100644
--- a/GPy/examples/tutorials.py
+++ b/GPy/examples/tutorials.py
@@ -138,7 +138,7 @@ def tuto_kernel_overview():
 
     k.constrain_positive('var')
     k.constrain_fixed(np.array([1]),1.75)
-    k.tie_param('len')
+    k.tie_params('len')
     k.unconstrain('white')
     k.constrain_bounded('white',lower=1e-5,upper=.5)
     print k
diff --git a/GPy/kern/__init__.py b/GPy/kern/__init__.py
index 132fad41..6852384c 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, prod, prod_orthogonal, symmetric, coregionalise
+from constructors import rbf, Matern32, Matern52, exponential, linear, white, bias, finite_dimensional, spline, Brownian, rbf_sympy, sympykern, periodic_exponential, periodic_Matern32, periodic_Matern52, prod, prod_orthogonal, symmetric, coregionalise, rational_quadratic
 from kern import kern
diff --git a/GPy/kern/constructors.py b/GPy/kern/constructors.py
index b848821b..983674b0 100644
--- a/GPy/kern/constructors.py
+++ b/GPy/kern/constructors.py
@@ -22,6 +22,7 @@ from prod import prod as prodpart
 from prod_orthogonal import prod_orthogonal as prod_orthogonalpart
 from symmetric import symmetric as symmetric_part
 from coregionalise import coregionalise as coregionalise_part
+from rational_quadratic import rational_quadratic as rational_quadraticpart
 #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.
 
@@ -280,3 +281,18 @@ def coregionalise(Nout,R=1, W=None, kappa=None):
     return kern(1,[p])
 
 
+def rational_quadratic(D,variance=1., lengthscale=1., power=1.):
+    """
+     Construct rational quadratic kernel.
+
+    :param D: the number of input dimensions
+    :type D: int (D=1 is the only value currently supported)
+    :param variance: the variance :math:`\sigma^2`
+    :type variance: float
+    :param lengthscale: the lengthscale :math:`\ell`
+    :type lengthscale: float
+    :rtype: kern object
+
+    """
+    part = rational_quadraticpart(D,variance, lengthscale, power)
+    return kern(D, [part])
diff --git a/GPy/kern/kern.py b/GPy/kern/kern.py
index b2970674..be45fa70 100644
--- a/GPy/kern/kern.py
+++ b/GPy/kern/kern.py
@@ -237,7 +237,7 @@ class kern(parameterised):
         for i in range(K1.Nparam + K2.Nparam):
             index = np.where(index_param==i)[0]
             if index.size > 1:
-                self.tie_param(index)
+                self.tie_params(index)
         for i in prev_constr_pos:
             self.constrain_positive(np.where(index_param==i)[0])
         for i in prev_constr_neg:
@@ -391,9 +391,13 @@ class kern(parameterised):
                 target += p2.variance*(p1._psi1[:,:,None]+p1._psi1[:,None,:])
             #linear X bias
             elif p1.name=='bias' and p2.name=='linear':
-                raise NotImplementedError
+                tmp = np.zeros((mu.shape[0],Z.shape[0]))
+                p2.psi1(Z,mu,S,tmp)
+                target += p1.variance*(tmp[:,:,None] + tmp[:,None,:])
             elif p2.name=='bias' and p1.name=='linear':
-                raise NotImplementedError
+                tmp = np.zeros((mu.shape[0],Z.shape[0]))
+                p1.psi1(Z,mu,S,tmp)
+                target += p2.variance*(tmp[:,:,None] + tmp[:,None,:])
             #rbf X linear
             elif p1.name=='linear' and p2.name=='rbf':
                 raise NotImplementedError #TODO
@@ -426,6 +430,11 @@ class kern(parameterised):
             elif p2.name=='bias' and p1.name=='rbf':
                 p1.dpsi1_dtheta(dL_dpsi2.sum(1)*p2.variance*2.,Z,mu,S,target[ps1])
                 p2.dpsi1_dtheta(dL_dpsi2.sum(1)*p1._psi1*2.,Z,mu,S,target[ps2])
+            #linear X bias
+            elif p1.name=='bias' and p2.name=='linear':
+                p2.dpsi1_dtheta(dL_dpsi2.sum(1)*p1.variance*2., Z, mu, S, target[ps1])
+            elif p2.name=='bias' and p1.name=='linear':
+                p1.dpsi1_dtheta(dL_dpsi2.sum(1)*p2.variance*2., Z, mu, S, target[ps1])
             #rbf X linear
             elif p1.name=='linear' and p2.name=='rbf':
                 raise NotImplementedError #TODO
@@ -451,6 +460,11 @@ class kern(parameterised):
                 p2.dpsi1_dX(dL_dpsi2.sum(1).T*p1.variance,Z,mu,S,target)
             elif p2.name=='bias' and p1.name=='rbf':
                 p1.dpsi1_dZ(dL_dpsi2.sum(1).T*p2.variance,Z,mu,S,target)
+            #linear X bias
+            elif p1.name=='bias' and p2.name=='linear':
+                p2.dpsi1_dZ(dL_dpsi2.sum(1).T*p1.variance, Z, mu, S, target)
+            elif p2.name=='bias' and p1.name=='linear':
+                p1.dpsi1_dZ(dL_dpsi2.sum(1).T*p2.variance, Z, mu, S, target)
             #rbf X linear
             elif p1.name=='linear' and p2.name=='rbf':
                 raise NotImplementedError #TODO
@@ -478,6 +492,11 @@ class kern(parameterised):
                 p2.dpsi1_dmuS(dL_dpsi2.sum(1).T*p1.variance*2.,Z,mu,S,target_mu,target_S)
             elif p2.name=='bias' and p1.name=='rbf':
                 p1.dpsi1_dmuS(dL_dpsi2.sum(1).T*p2.variance*2.,Z,mu,S,target_mu,target_S)
+            #linear X bias
+            elif p1.name=='bias' and p2.name=='linear':
+                p2.dpsi1_dmuS(dL_dpsi2.sum(1).T*p1.variance*2., Z, mu, S, target_mu, target_S)
+            elif p2.name=='bias' and p1.name=='linear':
+                p1.dpsi1_dmuS(dL_dpsi2.sum(1).T*p2.variance*2., Z, mu, S, target_mu, target_S)
             #rbf X linear
             elif p1.name=='linear' and p2.name=='rbf':
                 raise NotImplementedError #TODO
diff --git a/GPy/kern/rational_quadratic.py b/GPy/kern/rational_quadratic.py
new file mode 100644
index 00000000..b71d1354
--- /dev/null
+++ b/GPy/kern/rational_quadratic.py
@@ -0,0 +1,79 @@
+# Copyright (c) 2012, GPy authors (see AUTHORS.txt).
+# Licensed under the BSD 3-clause license (see LICENSE.txt)
+
+
+from kernpart import kernpart
+import numpy as np
+
+class rational_quadratic(kernpart):
+    """
+    rational quadratic kernel
+
+    .. math::
+
+       k(r) = \sigma^2 \left(1 + \frac{r^2}{2 \ell^2})^{- \alpha} \ \ \ \ \  \\text{ where  } r^2 = (x-y)^2
+
+    :param D: the number of input dimensions
+    :type D: int (D=1 is the only value currently supported)
+    :param variance: the variance :math:`\sigma^2`
+    :type variance: float
+    :param lengthscale: the lengthscale :math:`\ell`
+    :type lengthscale: float
+    :rtype: kernpart object
+
+    """
+    def __init__(self,D,variance=1.,lengthscale=1.,power=1.):
+        assert D == 1, "For this kernel we assume D=1"
+        self.D = D
+        self.Nparam = 3
+        self.name = 'rat_quad'
+        self.variance = variance
+        self.lengthscale = lengthscale
+        self.power = power
+
+    def _get_params(self):
+        return np.hstack((self.variance,self.lengthscale,self.power))
+
+    def _set_params(self,x):
+        self.variance = x[0]
+        self.lengthscale = x[1]
+        self.power = x[2]
+
+    def _get_param_names(self):
+        return ['variance','lengthscale','power']
+
+    def K(self,X,X2,target):
+        if X2 is None: X2 = X
+        dist2 = np.square((X-X2.T)/self.lengthscale)
+        target += self.variance*(1 + dist2/2.)**(-self.power)
+
+    def Kdiag(self,X,target):
+        target += self.variance
+
+    def dK_dtheta(self,dL_dK,X,X2,target):
+        if X2 is None: X2 = X
+        dist2 = np.square((X-X2.T)/self.lengthscale)
+
+        dvar = (1 + dist2/2.)**(-self.power)
+        dl = self.power * self.variance * dist2 * self.lengthscale**(-3) * (1 + dist2/2./self.power)**(-self.power-1)
+        dp = - self.variance * np.log(1 + dist2/2.) * (1 + dist2/2.)**(-self.power)
+
+        target[0] += np.sum(dvar*dL_dK)
+        target[1] += np.sum(dl*dL_dK)
+        target[2] += np.sum(dp*dL_dK)
+
+    def dKdiag_dtheta(self,dL_dKdiag,X,target):
+        target[0] += np.sum(dL_dKdiag)
+        # here self.lengthscale and self.power have no influence on Kdiag so target[1:] are unchanged
+
+    def dK_dX(self,dL_dK,X,X2,target):
+        """derivative of the covariance matrix with respect to X."""
+        if X2 is None: X2 = X
+        dist2 = np.square((X-X2.T)/self.lengthscale)
+
+        dX = -self.variance*self.power * (X-X2.T)/self.lengthscale**2 *  (1 + dist2/2./self.power)**(-self.power-1)
+        target += np.sum(dL_dK*dX)
+
+    def dKdiag_dX(self,dL_dKdiag,X,target):
+        pass
+    
diff --git a/GPy/kern/rbf.py b/GPy/kern/rbf.py
index 3c3d59e6..133895ff 100644
--- a/GPy/kern/rbf.py
+++ b/GPy/kern/rbf.py
@@ -55,6 +55,7 @@ class rbf(kernpart):
         self._X, self._X2, self._params = np.empty(shape=(3,1))
 
     def _get_params(self):
+        foo
         return np.hstack((self.variance,self.lengthscale))
 
     def _set_params(self,x):
diff --git a/GPy/models/BGPLVM.py b/GPy/models/Bayesian_GPLVM.py
similarity index 100%
rename from GPy/models/BGPLVM.py
rename to GPy/models/Bayesian_GPLVM.py
diff --git a/GPy/models/__init__.py b/GPy/models/__init__.py
index c099d0d5..22aa803c 100644
--- a/GPy/models/__init__.py
+++ b/GPy/models/__init__.py
@@ -10,4 +10,4 @@ from GPLVM import GPLVM
 from warped_GP import warpedGP
 from sparse_GPLVM import sparse_GPLVM
 from uncollapsed_sparse_GP import uncollapsed_sparse_GP
-from BGPLVM import Bayesian_GPLVM
+from Bayesian_GPLVM import Bayesian_GPLVM
diff --git a/GPy/testing/bgplvm_tests.py b/GPy/testing/bgplvm_tests.py
index dda92b90..b182c1a8 100644
--- a/GPy/testing/bgplvm_tests.py
+++ b/GPy/testing/bgplvm_tests.py
@@ -58,7 +58,7 @@ class BGPLVMTests(unittest.TestCase):
         m.randomize()
         self.assertTrue(m.checkgrad())
 
-    @unittest.skip('psi2 cross terms are NotImplemented for this combination')
+    #@unittest.skip('psi2 cross terms are NotImplemented for this combination')
     def test_linear_bias_kern(self):
         N, M, Q, D = 10, 3, 2, 4
         X = np.random.rand(N, Q)
diff --git a/GPy/testing/kernel_tests.py b/GPy/testing/kernel_tests.py
index bb809ea6..f1762db8 100644
--- a/GPy/testing/kernel_tests.py
+++ b/GPy/testing/kernel_tests.py
@@ -8,7 +8,7 @@ import GPy
 class KernelTests(unittest.TestCase):
     def test_kerneltie(self):
         K = GPy.kern.rbf(5, ARD=True)
-        K.tie_param('[01]')
+        K.tie_params('[01]')
         K.constrain_fixed('2')
         X = np.random.rand(5,5)
         Y = np.ones((5,1))