Added note on parameter types to ErrorMeasure and LogPDF

pints/_error_measures.py

@@ -17,7 +17,8 @@ class ErrorMeasure(object):
 
     ErrorMeasures are callable objects: If ``e`` is an instance of an
     :class:`ErrorMeasure` class you can calculate the error by calling ``e(p)``
-    where ``p`` is a point in parameter space.
+    where ``p`` is a point in parameter space. In PINTS, all parameters must be
+    continuous and real.
     """
     def __call__(self, x):
         raise NotImplementedError

pints/_log_pdfs.py

@@ -16,7 +16,8 @@ class LogPDF(object):
     All :class:`LogPDF` types are callable: when called with a vector argument
     ``p`` they return some value ``log(f(p))`` where ``f(p)`` is an
     unnormalised PDF. The size of the argument ``p`` is given by
-    :meth:`n_parameters()`.
+    :meth:`n_parameters()`. In PINTS, all parameters must be continuous and
+    real.
     """
     def __call__(self, x):
         raise NotImplementedError