Modifications to transformations ... not sure which tests to run to make sure I haven't messed things up. New code avoids exponentiating values greater than -log(eps) or less than log(eps). Also changed negative code to call the positive code (I think they should inherit the positive code ... but maybe not.

GPy/core/transformations.py

@@ -4,6 +4,8 @@
 
 import numpy as np
 from GPy.core.domains import POSITIVE, NEGATIVE, BOUNDED
+import sys 
+lim_val = -np.log(sys.float_info.epsilon) 
 
 class transformation(object):
     domain = None
@@ -17,7 +19,7 @@ class transformation(object):
         """ df_dx evaluated at self.f(x)=f"""
         raise NotImplementedError
     def initialize(self, f):
-        """ produce a sensible initial values for f(x)"""
+        """ produce a sensible initial value for f(x)"""
         raise NotImplementedError
     def __str__(self):
         raise NotImplementedError
@@ -25,13 +27,14 @@ class transformation(object):
 class logexp(transformation):
     domain = POSITIVE
     def f(self, x):
-        return np.log(1. + np.exp(x))
+        return np.where(x>lim_val, x, np.log(1. + np.exp(x)))
     def finv(self, f):
-        return np.log(np.exp(f) - 1.)
+        return np.where(f>lim_val, f, np.log(np.exp(f) - 1.))
     def gradfactor(self, f):
-        ef = np.exp(f)
-        return (ef - 1.) / ef
+        return np.where(f>lim_val, 1., 1 - np.exp(-f))
     def initialize(self, f):
+        if np.any(f < 0.):
+            print "Warning: changing parameters to satisfy constraints"
         return np.abs(f)
     def __str__(self):
         return '(+ve)'
@@ -39,18 +42,19 @@ class logexp(transformation):
 class negative_logexp(transformation):
     domain = NEGATIVE
     def f(self, x):
-        return -np.log(1. + np.exp(x))
+        return -logexp.f(x) #np.log(1. + np.exp(x))
     def finv(self, f):
-        return np.log(np.exp(-f) - 1.)
+        return logexp.finv(-f) #np.log(np.exp(-f) - 1.)
     def gradfactor(self, f):
-        ef = np.exp(-f)
-        return -(ef - 1.) / ef
+        return -logexp.gradfactor(-f)
+        #ef = np.exp(-f)
+        #return -(ef - 1.) / ef
     def initialize(self, f):
-        return -np.abs(f)
+        return -logexp.initialize(f) #np.abs(f)
     def __str__(self):
         return '(-ve)'
 
-class logexp_clipped(transformation):
+class logexp_clipped(logexp):
     max_bound = 1e100
     min_bound = 1e-10
     log_max_bound = np.log(max_bound)
@@ -78,9 +82,10 @@ class logexp_clipped(transformation):
         return '(+ve_c)'
 
 class exponent(transformation):
+    # TODO: can't allow this to go to zero, need to set a lower bound. Similar with negative exponent below. See old MATLAB code.
     domain = POSITIVE
     def f(self, x):
-        return np.exp(x)
+        return np.where(x<lim_val, np.where(x>-lim_val, np.exp(x), np.exp(-lim_val)), np.exp(lim_val))
     def finv(self, x):
         return np.log(x)
     def gradfactor(self, f):
@@ -92,18 +97,16 @@ class exponent(transformation):
     def __str__(self):
         return '(+ve)'
 
-class negative_exponent(transformation):
+class negative_exponent(exponent):
     domain = NEGATIVE
     def f(self, x):
-        return -np.exp(x)
-    def finv(self, x):
-        return np.log(-x)
+        return -exponent.f(x)
+    def finv(self, f):
+        return exponent.finv(-f)
     def gradfactor(self, f):
         return f
     def initialize(self, f):
-        if np.any(f > 0.):
-            print "Warning: changing parameters to satisfy constraints"
-        return -np.abs(f)
+        return -exponent.initialize(f) #np.abs(f)
     def __str__(self):
         return '(-ve)'
 

GPy/kern/constructors.py

@@ -51,6 +51,24 @@ def linear(input_dim,variances=None,ARD=False):
     part = parts.linear.Linear(input_dim,variances,ARD)
     return kern(input_dim, [part])
 
+def mlp(input_dim,variance=1., weight_variance=None,bias_variance=100.,ARD=False):
+    """
+    Construct an MLP kernel
+
+    :param input_dim: dimensionality of the kernel, obligatory
+    :type input_dim: int
+    :param variance: the variance of the kernel
+    :type variance: float
+    :param weight_scale: the lengthscale of the kernel
+    :type weight_scale: vector of weight variances for input weights in neural network (length 1 if kernel is isotropic)
+    :param bias_variance: the variance of the biases in the neural network.
+    :type bias_variance: float
+    :param ARD: Auto Relevance Determination (allows for ARD version of covariance)
+    :type ARD: Boolean
+    """
+    part = parts.mlp.MLP(input_dim,variance,weight_variance,bias_variance,ARD)
+    return kern(input_dim, [part])
+
 def white(input_dim,variance=1.):
     """
      Construct a white kernel.
@@ -253,6 +271,8 @@ def prod(k1,k2,tensor=False):
 
     :param k1, k2: the kernels to multiply
     :type k1, k2: kernpart
+    :param tensor: The kernels are either multiply as functions defined on the same input space (default) or on the product of the input spaces
+    :type tensor: Boolean
     :rtype: kernel object
     """
     part = parts.prod.Prod(k1, k2, tensor)
@@ -260,13 +280,13 @@ def prod(k1,k2,tensor=False):
 
 def symmetric(k):
     """
-    Construct a symmetrical kernel from an existing kernel
+    Construct a symmetric kernel from an existing kernel
     """
     k_ = k.copy()
     k_.parts = [symmetric.Symmetric(p) for p in k.parts]
     return k_
 
-def coregionalise(Nout,R=1, W=None, kappa=None):
+def coregionalise(Nout, R=1, W=None, kappa=None):
     p = parts.coregionalise.Coregionalise(Nout,R,W,kappa)
     return kern(1,[p])
 
@@ -291,11 +311,13 @@ def fixed(input_dim, K, variance=1.):
     """
      Construct a Fixed effect kernel.
 
-     Arguments
-     ---------
-     input_dim (int), obligatory
-     K (np.array), obligatory
-     variance (float)
+    :param input_dim: the number of input dimensions
+    :type input_dim: int (input_dim=1 is the only value currently supported)
+    :param K: the variance :math:`\sigma^2`
+    :type K: np.array
+    :param variance: kernel variance
+    :type variance: float
+    :rtype: kern object
     """
     part = parts.fixed.Fixed(input_dim, K, variance)
     return kern(input_dim, [part])
@@ -318,7 +340,7 @@ def independent_outputs(k):
 
 def hierarchical(k):
     """
-    Construct a kernel with independent outputs from an existing kernel
+    TODO THis can't be right! Construct a kernel with independent outputs from an existing kernel
     """
     # for sl in k.input_slices:
     #     assert (sl.start is None) and (sl.stop is None), "cannot adjust input slices! (TODO)"

GPy/kern/parts/__init__.py

@@ -8,6 +8,7 @@ import independent_outputs
 import linear
 import Matern32
 import Matern52
+import mlp
 import periodic_exponential
 import periodic_Matern32
 import periodic_Matern52

GPy/models/gp_regression.py

@@ -37,7 +37,6 @@ class GPRegression(GP):
     def getstate(self):
         return GP.getstate(self)
 
-
     def setstate(self, state):
         return GP.setstate(self, state)
 

GPy/testing/unit_tests.py

@@ -59,6 +59,11 @@ class GradientTests(unittest.TestCase):
         k = GPy.kern.rbf(2, ARD=True)
         self.check_model_with_white(k, model_type='GPRegression', dimension=2)
 
+    def test_GPRegression_mlp_1d(self):
+        ''' Testing the GP regression with mlp kernel with white kernel on 1d data '''
+        mlp = GPy.kern.mlp(1)
+        self.check_model_with_white(mlp, model_type='GPRegression', dimension=1)
+
     def test_GPRegression_matern52_1D(self):
         ''' Testing the GP regression with matern52 kernel on 1d data '''
         matern52 = GPy.kern.Matern52(1)