Fix Scalar multiplication

nifty5/models/model.py

@@ -57,7 +57,7 @@ class Model(NiftyMetaBase()):
 
     def __mul__(self, other):
         if isinstance(other, (float, int)):
-            return ScalarMul(self._position, other, self)
+            return ScalarMul(other, self)
         if isinstance(other, Model):
             return Mul.make(self, other)
         raise NotImplementedError
@@ -127,21 +127,19 @@ class Add(Model):
 
 
 class ScalarMul(Model):
-    def __init__(self, position, factor, op):
-        super(ScalarMul, self).__init__(position)
+    def __init__(self, factor, op):
+        super(ScalarMul, self).__init__(op.position)
         if not isinstance(factor, (float, int)):
             raise TypeError
-        if not isinstance(op, Model):
-            raise TypeError
 
-        self._op = op.at(position)
+        self._op = op
         self._factor = factor
 
         self._value = self._factor * self._op.value
         self._gradient = self._factor * self._op.gradient
 
     def at(self, position):
-        return self.__class__(position, self._factor, self._op)
+        return self.__class__(self._factor, self._op.at(position))
 
 
 class LinearModel(Model):