add regularization

urbansim/models/dcm.py

@@ -243,6 +243,10 @@ class MNLDiscreteChoiceModel(DiscreteChoiceModel):
         in output.
     normalize : bool, optional default False
         subtract the mean and divide by the standard deviation before fitting the Coefficients
+    l1 : float, optional default 0.0
+        the amount of l1 (Lasso) regularization when fitting the Coefficients
+    l2 : float, optional default 0.0
+        the amount of l2 (Ridge) regularization when fitting the Coefficients
 
     """
     def __init__(
@@ -254,7 +258,7 @@ def __init__(
             estimation_sample_size=None,
             prediction_sample_size=None,
             choice_column=None, name=None,
-            normalize=False):
+            normalize=False, l1=0.0, l2=0.0):
         self._check_prob_choice_mode_compat(probability_mode, choice_mode)
         self._check_prob_mode_interaction_compat(
             probability_mode, interaction_predict_filters)
@@ -274,6 +278,8 @@ def __init__(
         self.name = name if name is not None else 'MNLDiscreteChoiceModel'
         self.sim_pdf = None
         self.normalize = normalize
+        self.l1 = l1
+        self.l2 = l2
 
         self.log_likelihoods = None
         self.fit_parameters = None
@@ -314,6 +320,8 @@ def from_yaml(cls, yaml_str=None, str_or_buffer=None):
             choice_column=cfg.get('choice_column', None),
             name=cfg.get('name', None),
             normalize=cfg.get('normalize', False),
+            l1=cfg.get('l1', 0.0),
+            l2=cfg.get('l2', 0.0),
         )
 
         if cfg.get('log_likelihoods', None):
@@ -425,7 +433,7 @@ def fit(self, choosers, alternatives, current_choice):
                 'the input columns.')
 
         self.log_likelihoods, self.fit_parameters = mnl.mnl_estimate(
-            model_design.as_matrix(), chosen, self.sample_size, self.normalize)
+            model_design.as_matrix(), chosen, self.sample_size, self.normalize, self.l1, self.l2)
         self.fit_parameters.index = model_design.columns
 
         logger.debug('finish: fit LCM model {}'.format(self.name))
@@ -702,6 +710,8 @@ def to_dict(self):
             'fit_parameters': (yamlio.frame_to_yaml_safe(self.fit_parameters)
                                if self.fitted else None),
             'normalize': self.normalize,
+            'l1': self.l1,
+            'l2': self.l2,
         }
 
     def to_yaml(self, str_or_buffer=None):

urbansim/urbanchoice/mnl.py

@@ -64,7 +64,7 @@ def get_standard_error(hessian):
 
 
 def mnl_loglik(beta, data, chosen, numalts, weights=None, lcgrad=False,
-               stderr=0):
+               stderr=0, l1=0.0, l2=0.0):
     logger.debug('start: calculate MNL log-likelihood')
     numvars = beta.size
     numobs = data.size() // numvars // numalts
@@ -114,6 +114,12 @@ def mnl_loglik(beta, data, chosen, numalts, weights=None, lcgrad=False,
         loglik = loglik.get_mat()[0, 0]
         gradarr = np.reshape(gradarr.get_mat(), (1, gradarr.size()))[0]
 
+    loglik -= l1 * np.abs(beta.get_mat()).sum()
+    gradarr -= l1 * np.sign(beta.get_mat())
+
+    loglik -= l2 * np.square(beta.get_mat()).sum()
+    gradarr -= l1 * beta.get_mat()
+
     logger.debug('finish: calculate MNL log-likelihood')
     return -1 * loglik, -1 * gradarr
 
@@ -178,7 +184,7 @@ def mnl_simulate(data, coeff, numalts, normalization_mean=0.0, normalization_std
 
 
 def mnl_estimate(data, chosen, numalts, GPU=False, coeffrange=(-3, 3),
-                 weights=None, lcgrad=False, beta=None, normalize=False):
+                 weights=None, lcgrad=False, beta=None, normalize=False, l1=0.0, l2=0.0):
     """
     Calculate coefficients of the MNL model.
 
@@ -249,7 +255,7 @@ def mnl_estimate(data, chosen, numalts, GPU=False, coeffrange=(-3, 3),
     bounds = [coeffrange] * numvars
 
     with log_start_finish('scipy optimization for MNL fit', logger):
-        args = (data, chosen, numalts, weights, lcgrad)
+        args = (data, chosen, numalts, weights, lcgrad, l1, l2)
         bfgs_result = scipy.optimize.fmin_l_bfgs_b(mnl_loglik,
                                                    beta,
                                                    args=args,