Add fixed ancestral size for structure model

gadma/cli/settings_storage.py

@@ -1342,6 +1342,14 @@ def get_model(self):
             )
             constrain = self.get_linear_constrain_for_model(model)
             model.linear_constrain = constrain
+            if self.fixed_ancestral_size:
+                if self.ancestral_size_as_parameter is not None:
+                    ValueError(
+                        "Option `Fixed ancestral size` is set, please set "
+                        "`Ancestral size as parameter` to True"
+                    )
+                model.fix_variable(model.Nanc_size, self.fixed_ancestral_size)
+                model.Nanc_size = self.fixed_ancestral_size
             return model
         elif ((self.custom_filename is not None or
                 self.model_func is not None) and
@@ -1787,6 +1795,24 @@ def is_valid(self):
                     "`Lower bound of second split` should be less than `Upper"
                     " bound of first split`"
                 )
+        if self.fixed_ancestral_size is not None:
+            # check that mu and L are given
+            if self.sequence_length is None:
+                raise ValueError(
+                    "`Sequence length` should be specified in order to use "
+                    "fixed ancestral size."
+                )
+            if self.mutation_rate is None:
+                raise ValueError(
+                    "`Mutation rate` should be specified in order to use "
+                    "fixed ancestral size."
+                )
+            if not self.ancestral_size_as_parameter:
+                self.ancestral_size_as_parameter = True
+                warnings.warn(
+                    "Option `Ancestral sizea as parameter` is set to True, "
+                    "as fixed ancestral population size is used."
+                )
 
     def print_citations(self):
         """

gadma/models/demographic_model.py

@@ -327,6 +327,10 @@ def fix_variable(self, variable, value):
         :param variable: Variable to fix.
         :param value: Value of the variable to fix.
         """
+        # check for ancestral population size
+        if variable == self.Nanc_size:
+            super(DemographicModel, self).fix_variable(variable, value)
+            return
         for event in self.events:
             if variable in event.variables:
                 event.fix_variable(variable, value)