added caching framework

GPy/util/caching.py

@@ -0,0 +1,41 @@
+import numpy as np
+from ..core.parameterization.array_core import ObservableArray
+class Cacher(object):
+    def __init__(self, operation, limit=5):
+        self.limit = int(limit)
+        self.operation=operation
+        self.cached_inputs = []
+        self.cached_outputs = []
+        self.inputs_changed = []
+
+    def __call__(self, X):
+        assert isinstance(X, ObservableArray)
+        if X in self.cached_inputs:
+            i = self.cached_inputs.index(X)
+            if self.inputs_changed[i]:
+                self.cached_outputs[i] = self.operation(X)
+                self.inputs_changed[i] = False
+            return self.cached_outputs[i]
+        else:
+            if len(self.cached_inputs) == self.limit:
+                X_ = self.cached_inputs.pop(0)
+                X_.remove_observer(self)
+                self.inputs_changed.pop(0)
+                self.cached_outputs.pop(0)
+
+            self.cached_inputs.append(X)
+            self.cached_outputs.append(self.operation(X))
+            self.inputs_changed.append(False)
+            X.add_observer(self, self.on_cache_changed)
+            return self.cached_outputs[-1]
+
+    def on_cache_changed(self, X):
+        print id(X)
+        i = self.cached_inputs.index(X)
+        self.inputs_changed[i] = True
+
+                
+
+
+
+