Fix/exp smooth constructor args (#2059)

* feat: adding support for constructor kwargs

* feat: adding tests

* fix: udpated representation test for ExponentialSmoothing model

* update changelog.md

---------

Co-authored-by: dennisbader <[email protected]>

Author: madtoinou

CHANGELOG.md

@@ -20,6 +20,7 @@ but cannot always guarantee backwards compatibility. Changes that may **break co
   - `XGBModel` now leverages XGBoost's native Quantile Regression support that was released in version 2.0.0 for improved probabilistic forecasts. [#2051](https://github.com/unit8co/darts/pull/2051) by [Dennis Bader](https://github.com/dennisbader).
 - Other improvements:
   - Added support for time index time zone conversion with parameter `tz` before generating/computing holidays and datetime attributes. Support was added to all Time Axis Encoders (standalone encoders and forecasting models' `add_encoders`, time series generation utils functions `holidays_timeseries()` and `datetime_attribute_timeseries()`, and `TimeSeries` methods `add_datetime_attribute()` and `add_holidays()`. [#2054](https://github.com/unit8co/darts/pull/2054) by [Dennis Bader](https://github.com/dennisbader).
+  - Added optional keyword arguments dict `kwargs` to `ExponentialSmoothing` that will be passed to the constructor of the underlying `statsmodels.tsa.holtwinters.ExponentialSmoothing` model. [#2059](https://github.com/unit8co/darts/pull/2059) by [Antoine Madrona](https://github.com/madtoinou).
 
 **Fixed**
 - Fixed a bug when calling optimized `historical_forecasts()` for a `RegressionModel` trained with unequal component-specific lags. [#2040](https://github.com/unit8co/darts/pull/2040) by [Antoine Madrona](https://github.com/madtoinou).

darts/models/forecasting/exponential_smoothing.py

@@ -3,7 +3,7 @@
 ---------------------
 """
 
-from typing import Optional
+from typing import Any, Dict, Optional
 
 import numpy as np
 import statsmodels.tsa.holtwinters as hw
@@ -24,7 +24,8 @@ def __init__(
         seasonal: Optional[SeasonalityMode] = SeasonalityMode.ADDITIVE,
         seasonal_periods: Optional[int] = None,
         random_state: int = 0,
-        **fit_kwargs,
+        kwargs: Optional[Dict[str, Any]] = None,
+        **fit_kwargs
     ):
 
         """Exponential Smoothing
@@ -61,6 +62,11 @@ def __init__(
         seasonal_periods
             The number of periods in a complete seasonal cycle, e.g., 4 for quarterly data or 7 for daily
             data with a weekly cycle. If not set, inferred from frequency of the series.
+        kwargs
+            Some optional keyword arguments that will be used to call
+            :func:`statsmodels.tsa.holtwinters.ExponentialSmoothing()`.
+            See `the documentation
+            <https://www.statsmodels.org/stable/generated/statsmodels.tsa.holtwinters.ExponentialSmoothing.html>`_.
         fit_kwargs
             Some optional keyword arguments that will be used to call
             :func:`statsmodels.tsa.holtwinters.ExponentialSmoothing.fit()`.
@@ -91,6 +97,7 @@ def __init__(
         self.seasonal = seasonal
         self.infer_seasonal_periods = seasonal_periods is None
         self.seasonal_periods = seasonal_periods
+        self.constructor_kwargs = dict() if kwargs is None else kwargs
         self.fit_kwargs = fit_kwargs
         self.model = None
         np.random.seed(random_state)
@@ -120,6 +127,7 @@ def fit(self, series: TimeSeries):
             seasonal_periods=seasonal_periods_param,
             freq=series.freq if series.has_datetime_index else None,
             dates=series.time_index if series.has_datetime_index else None,
+            **self.constructor_kwargs
         )
         hw_results = hw_model.fit(**self.fit_kwargs)
         self.model = hw_results

darts/tests/models/forecasting/test_exponential_smoothing.py

@@ -1,41 +1,92 @@
 import numpy as np
+import pytest
 
 from darts import TimeSeries
 from darts.models import ExponentialSmoothing
 from darts.utils import timeseries_generation as tg
 
 
 class TestExponentialSmoothing:
-    def helper_test_seasonality_inference(self, freq_string, expected_seasonal_periods):
-        series = tg.sine_timeseries(length=200, freq=freq_string)
-        model = ExponentialSmoothing()
-        model.fit(series)
-        assert model.seasonal_periods == expected_seasonal_periods
+    series = tg.sine_timeseries(length=100, freq="H")
 
-    def test_seasonality_inference(self):
-
-        # test `seasonal_periods` inference for datetime indices
-        freq_str_seasonality_periods_tuples = [
+    @pytest.mark.parametrize(
+        "freq_string,expected_seasonal_periods",
+        [
             ("D", 7),
             ("H", 24),
             ("M", 12),
             ("W", 52),
             ("Q", 4),
             ("B", 5),
-        ]
-        for tuple in freq_str_seasonality_periods_tuples:
-            self.helper_test_seasonality_inference(*tuple)
+        ],
+    )
+    def test_seasonality_inference(
+        self, freq_string: str, expected_seasonal_periods: int
+    ):
+        series = tg.sine_timeseries(length=200, freq=freq_string)
+        model = ExponentialSmoothing()
+        model.fit(series)
+        assert model.seasonal_periods == expected_seasonal_periods
 
-        # test default selection for integer index
+    def test_default_parameters(self):
+        """Test default selection for integer index"""
         series = TimeSeries.from_values(np.arange(1, 30, 1))
         model = ExponentialSmoothing()
         model.fit(series)
         assert model.seasonal_periods == 12
 
-        # test whether a model that inferred a seasonality period before will do it again for a new series
+    def test_multiple_fit(self):
+        """Test whether a model that inferred a seasonality period before will do it again for a new series"""
         series1 = tg.sine_timeseries(length=100, freq="M")
         series2 = tg.sine_timeseries(length=100, freq="D")
         model = ExponentialSmoothing()
         model.fit(series1)
         model.fit(series2)
         assert model.seasonal_periods == 7
+
+    def test_constructor_kwargs(self):
+        """Using kwargs to pass additional parameters to the constructor"""
+        constructor_kwargs = {
+            "initialization_method": "known",
+            "initial_level": 0.5,
+            "initial_trend": 0.2,
+            "initial_seasonal": np.arange(1, 25),
+        }
+        model = ExponentialSmoothing(kwargs=constructor_kwargs)
+        model.fit(self.series)
+        # must be checked separately, name is not consistent
+        np.testing.assert_array_almost_equal(
+            model.model.model.params["initial_seasons"],
+            constructor_kwargs["initial_seasonal"],
+        )
+        for param_name in ["initial_level", "initial_trend"]:
+            assert (
+                model.model.model.params[param_name] == constructor_kwargs[param_name]
+            )
+
+    def test_fit_kwargs(self):
+        """Using kwargs to pass additional parameters to the fit()"""
+        # using default optimization method
+        model = ExponentialSmoothing()
+        model.fit(self.series)
+        assert model.fit_kwargs == {}
+        pred = model.predict(n=2)
+
+        model_bis = ExponentialSmoothing()
+        model_bis.fit(self.series)
+        assert model_bis.fit_kwargs == {}
+        pred_bis = model_bis.predict(n=2)
+
+        # two methods with the same parameters should yield the same forecasts
+        assert pred.time_index.equals(pred_bis.time_index)
+        np.testing.assert_array_almost_equal(pred.values(), pred_bis.values())
+
+        # change optimization method
+        model_ls = ExponentialSmoothing(method="least_squares")
+        model_ls.fit(self.series)
+        assert model_ls.fit_kwargs == {"method": "least_squares"}
+        pred_ls = model_ls.predict(n=2)
+
+        # forecasts should be slightly different
+        assert pred.time_index.equals(pred_ls.time_index)
+        assert all(np.not_equal(pred.values(), pred_ls.values()))

darts/tests/models/forecasting/test_local_forecasting_models.py

@@ -651,7 +651,7 @@ def test_model_str_call(self, config):
             (
                 ExponentialSmoothing(),
                 "ExponentialSmoothing(trend=ModelMode.ADDITIVE, damped=False, seasonal=SeasonalityMode.ADDITIVE, "
-                + "seasonal_periods=None, random_state=0)",
+                + "seasonal_periods=None, random_state=0, kwargs=None)",
             ),  # no params changed
             (
                 ARIMA(1, 1, 1),