Fix logic of Inversion.__next__ method (#55)

The first model that gets returned should be the initial model, so the
zeroth model matches the zeroth iteration (status before any
minimization is carried out). This would also make the list of models
generated by the iterator the same as the `Inversion.models`.

Author: santisoler

src/inversion_ideas/inversion.py

@@ -87,20 +87,27 @@ def __init__(
         self.model = initial_model.copy()
 
         # Initialize the counter
-        if not hasattr(self, "_counter"):
-            self._counter = 0
+        self._counter = 0
 
     def __next__(self):
         """
         Run next iteration in the inversion.
         """
-        if self.counter == 0 and self.log is not None:
+        if self.counter == 0:
             # Add initial model to log (only on zeroth iteration)
-            self.log.update(self.counter, self.model)
+            if self.log is not None:
+                self.log.update(self.counter, self.model)
+
             # Initialize stopping criteria (if necessary)
             if hasattr(self.stopping_criteria, "initialize"):
                 self.stopping_criteria.initialize()
 
+            # Increase counter by one
+            self._counter += 1
+
+            # Return the initial model in the zeroth iteration
+            return self.model
+
         # Check for stopping criteria before trying to run the iteration
         if self.stopping_criteria(self.model):
             get_logger().info(
@@ -124,9 +131,8 @@ def __next__(self):
         # We update the directives here (and not at the end of this method), so after
         # each iteration the objective function is still the same we passed to the
         # minimizer.
-        if self.counter > 0:
-            for directive in self.directives:
-                directive(self.model, self.counter)
+        for directive in self.directives:
+            directive(self.model, self.counter)
 
         # Minimize objective function
         if isinstance(self.minimizer, Minimizer):