renamed sd to sigma in pymc/model.py

Author: purna135

pymc/model.py

@@ -482,7 +482,7 @@ def __init__(self, mean=0, sigma=1, name=''):
                 Normal('v2', mu=mean, sigma=sd)
 
                 # something more complex is allowed, too
-                half_cauchy = HalfCauchy('sd', beta=10, initval=1.)
+                half_cauchy = HalfCauchy('sigma', beta=10, initval=1.)
                 Normal('v3', mu=mean, sigma=half_cauchy)
 
                 # Deterministic variables can be used in usual way