Added capability for sinc covariance via sympy kernel.

GPy/util/symbolic.py

@@ -0,0 +1,32 @@
+from sympy import Function, S, oo, I, cos, sin
+
+
+class sinc_grad(Function):
+    nargs = 1
+    
+    def fdiff(self, argindex=1):
+        return ((2-x*x)*sin(self.args[0]) - 2*x*cos(x))/(x*x*x)
+    
+    @classmethod
+    def eval(cls, x):
+        if x is S.Zero:
+            return S.Zero
+        else:
+            return (x*cos(x) - sin(x))/(x*x)
+            
+class sinc(Function):
+    
+    nargs = 1
+    
+    def fdiff(self, argindex=1):
+        return sinc_grad(self.args[0])
+    
+    @classmethod
+    def eval(cls, x):
+        if x is S.Zero:
+            return S.One
+        else:
+            return sin(x)/x
+    
+    def _eval_is_real(self):
+        return self.args[0].is_real