feat: automatic windowing procedure can now be deactivated by choosing

S=0

pyerrors/__init__.py

@@ -98,6 +98,9 @@ my_sum.details()
 
 The integrated autocorrelation time $\tau_\mathrm{int}$ and the autocorrelation function $\rho(W)$ can be monitored via the methods `pyerrors.obs.Obs.plot_tauint` and `pyerrors.obs.Obs.plot_tauint`.
 
+If the parameter $S$ is set to zero it is assumed that dataset does not exhibit any autocorrelation and the windowsize is chosen to be zero.
+In this case the error estimate is identical to the sample standard error.
+
 ### Exponential tails
 
 Slow modes in the Monte Carlo history can be accounted for by attaching an exponential tail to the autocorrelation function $\rho$ as suggested in [arXiv:1009.5228](https://arxiv.org/abs/1009.5228). The longest autocorrelation time in the history, $\tau_\mathrm{exp}$, can be passed to the `gamma_method` as parameter. In this case the automatic windowing procedure is vacated and the parameter $S$ does not affect the error estimate.

pyerrors/obs.py

@@ -155,20 +155,21 @@ class Obs:
         return res
 
     def gamma_method(self, **kwargs):
-        """Calculate the error and related properties of the Obs.
+        """Estimate the error and related properties of the Obs.
 
         Parameters
         ----------
         S : float
-            specifies a custom value for the parameter S (default 2.0), can be
-            a float or an array of floats for different ensembles
+            specifies a custom value for the parameter S (default 2.0).
+            If set to 0 it is assumed that the data exhibits no
+            autocorrelation. In this case the error estimates coincides
+            with the sample standard error.
         tau_exp : float
             positive value triggers the critical slowing down analysis
-            (default 0.0), can be a float or an array of floats for different
-            ensembles
+            (default 0.0).
         N_sigma : float
             number of standard deviations from zero until the tail is
-            attached to the autocorrelation function (default 1)
+            attached to the autocorrelation function (default 1).
         fft : bool
             determines whether the fft algorithm is used for the computation
             of the autocorrelation function (default True)
@@ -281,19 +282,26 @@ class Obs:
                         self.e_windowsize[e_name] = n
                         break
             else:
-                # Standard automatic windowing procedure
-                g_w = self.S[e_name] / np.log((2 * self.e_n_tauint[e_name][1:] + 1) / (2 * self.e_n_tauint[e_name][1:] - 1))
-                g_w = np.exp(- np.arange(1, w_max) / g_w) - g_w / np.sqrt(np.arange(1, w_max) * e_N)
-                for n in range(1, w_max):
-                    if n < w_max // 2 - 2:
-                        _compute_drho(n + 1)
-                    if g_w[n - 1] < 0 or n >= w_max - 1:
-                        self.e_tauint[e_name] = self.e_n_tauint[e_name][n] * (1 + (2 * n + 1) / e_N) / (1 + 1 / e_N)  # Bias correction hep-lat/0306017 eq. (49)
-                        self.e_dtauint[e_name] = self.e_n_dtauint[e_name][n]
-                        self.e_dvalue[e_name] = np.sqrt(2 * self.e_tauint[e_name] * e_gamma[e_name][0] * (1 + 1 / e_N) / e_N)
-                        self.e_ddvalue[e_name] = self.e_dvalue[e_name] * np.sqrt((n + 0.5) / e_N)
-                        self.e_windowsize[e_name] = n
-                        break
+                if self.S[e_name] == 0.0:
+                    self.e_tauint[e_name] = 0.5
+                    self.e_dtauint[e_name] = 0.0
+                    self.e_dvalue[e_name] = np.sqrt(e_gamma[e_name][0] / (e_N - 1))
+                    self.e_ddvalue[e_name] = self.e_dvalue[e_name] * np.sqrt(0.5 / e_N)
+                    self.e_windowsize[e_name] = 0
+                else:
+                    # Standard automatic windowing procedure
+                    tau = self.S[e_name] / np.log((2 * self.e_n_tauint[e_name][1:] + 1) / (2 * self.e_n_tauint[e_name][1:] - 1))
+                    g_w = np.exp(- np.arange(1, w_max) / tau) - tau / np.sqrt(np.arange(1, w_max) * e_N)
+                    for n in range(1, w_max):
+                        if n < w_max // 2 - 2:
+                            _compute_drho(n + 1)
+                        if g_w[n - 1] < 0 or n >= w_max - 1:
+                            self.e_tauint[e_name] = self.e_n_tauint[e_name][n] * (1 + (2 * n + 1) / e_N) / (1 + 1 / e_N)  # Bias correction hep-lat/0306017 eq. (49)
+                            self.e_dtauint[e_name] = self.e_n_dtauint[e_name][n]
+                            self.e_dvalue[e_name] = np.sqrt(2 * self.e_tauint[e_name] * e_gamma[e_name][0] * (1 + 1 / e_N) / e_N)
+                            self.e_ddvalue[e_name] = self.e_dvalue[e_name] * np.sqrt((n + 0.5) / e_N)
+                            self.e_windowsize[e_name] = n
+                            break
 
             self._dvalue += self.e_dvalue[e_name] ** 2
             self.ddvalue += (self.e_dvalue[e_name] * self.e_ddvalue[e_name]) ** 2

tests/obs_test.py

@@ -95,6 +95,18 @@ def test_gamma_method():
         assert test_obs.e_tauint['t'] - 10.5 <= test_obs.e_dtauint['t']
 
 
+def test_gamma_method_no_windowing():
+    for iteration in range(50):
+        obs = pe.Obs([np.random.normal(1.02, 0.02, 733 + np.random.randint(1000))], ['ens'])
+        obs.gamma_method(S=0)
+        assert obs.e_tauint['ens'] == 0.5
+        assert np.isclose(np.sqrt(np.var(obs.deltas['ens'], ddof=1) / obs.shape['ens']), obs.dvalue)
+        obs.gamma_method(S=1.1)
+        assert obs.e_tauint['ens'] > 0.5
+    with pytest.raises(Exception):
+        obs.gamma_method(S=-0.2)
+
+
 def test_gamma_method_persistance():
     my_obs = pe.Obs([np.random.rand(730)], ['t'])
     my_obs.gamma_method()