addint constant mapping

GPy/mappings/constant.py

@@ -0,0 +1,40 @@
+# Copyright (c) 2015, James Hensman, Alan Saul
+import numpy as np
+from ..core.mapping import Mapping
+from ..core.parameterization import Param
+
+class Constant(Mapping):
+    """
+    A Linear mapping.
+
+    .. math::
+
+       F(\mathbf{x}) = c
+
+
+    :param input_dim: dimension of input.
+    :type input_dim: int
+    :param output_dim: dimension of output.
+    :type output_dim: int
+    :param: value the value of this constant mapping
+
+    """
+
+    def __init__(self, input_dim, output_dim, value=0., name='linmap'):
+        Mapping.__init__(self, input_dim=input_dim, output_dim=output_dim, name=name)
+        value = np.atleast_1d(value)
+        if not len(value.shape) ==1:
+            raise ValueError("bad constant values: pass a float or flat vectoor")
+        elif value.size==1:
+            value = np.ones(self.output_dim)*value
+        self.C = Param('C', value)
+        self.link_parameter(self.C)
+
+    def f(self, X):
+        return np.tile(self.C.values[None,:], (X.shape[0], 1))
+
+    def update_gradients(self, dL_dF, X):
+        self.C.gradient = 0.
+
+    def gradients_X(self, dL_dF, X):
+        return np.zeros_like(X)