Set standard for delta

nifty5/library/inverse_gamma_model.py

@@ -30,7 +30,7 @@ from ..sugar import makeOp
 
 
 class InverseGammaModel(Operator):
-    def __init__(self, domain, alpha, q, delta):
+    def __init__(self, domain, alpha, q, delta=0.001):
         """Model which transforms a Gaussian into an inverse gamma distribution.
 
         The pdf of the inverse gamma distribution is defined as follows: