added full_output option to non gaussian parameter so that correct statistics can be done afterwards

src/mdevaluate/correlation.py

@@ -18,7 +18,7 @@ def log_indices(first: int, last: int, num: int = 100) -> np.ndarray:
     return np.unique(np.int_(ls) - 1 + first)
 
 
-@autosave_data(2)
+@autosave_data(nargs=2, kwargs_keys=('selector', 'segments', 'skip', 'window', 'average', 'points',), version=1.0)
 def shifted_correlation(
     function: Callable,
     frames: Coordinates,
@@ -199,7 +199,7 @@ def msd(
         raise ValueError('Parameter axis has to be ether "all", "x", "y", or "z"!')
 
 
-def isf(
+def isf_raw(
     start_frame: CoordinateFrame,
     end_frame: CoordinateFrame,
     q: float = 22.7,
@@ -216,29 +216,59 @@ def isf(
         displacements = displacements_without_drift(start_frame, end_frame, trajectory)
     if axis == "all":
         distance = (displacements**2).sum(axis=1) ** 0.5
-        return np.sinc(distance * q / np.pi).mean()
+        return np.sinc(distance * q / np.pi)
     elif axis == "xy" or axis == "yx":
         distance = (displacements[:, [0, 1]]**2).sum(axis=1) ** 0.5
-        return np.real(jn(0, distance * q)).mean()
+        return np.real(jn(0, distance * q))
     elif axis == "xz" or axis == "zx":
         distance = (displacements[:, [0, 2]]**2).sum(axis=1) ** 0.5
-        return np.real(jn(0, distance * q)).mean()
+        return np.real(jn(0, distance * q))
     elif axis == "yz" or axis == "zy":
         distance = (displacements[:, [1, 2]]**2).sum(axis=1) ** 0.5
-        return np.real(jn(0, distance * q)).mean()
+        return np.real(jn(0, distance * q))
     elif axis == "x":
         distance = np.abs(displacements[:, 0])
-        return np.mean(np.cos(np.abs(q * distance)))
+        return np.cos(np.abs(q * distance))
     elif axis == "y":
         distance = np.abs(displacements[:, 1])
-        return np.mean(np.cos(np.abs(q * distance)))
+        return np.cos(np.abs(q * distance))
     elif axis == "z":
         distance = np.abs(displacements[:, 2])
-        return np.mean(np.cos(np.abs(q * distance)))
+        return np.cos(np.abs(q * distance))
     else:
         raise ValueError('Parameter axis has to be ether "all", "x", "y", or "z"!')
 
 
+def isf(
+    start_frame: CoordinateFrame,
+    end_frame: CoordinateFrame,
+    q: float = 22.7,
+    trajectory: Coordinates = None,
+    axis: str = "all",
+) -> float:
+    """
+    Incoherent intermediate scattering function averaged over all particles.
+    See isf_raw for details.
+    """
+    return isf_raw(start_frame, end_frame, q=q, trajectory=trajectory, axis=axis).mean()
+
+
+def isf_mean_var(
+    start_frame: CoordinateFrame,
+    end_frame: CoordinateFrame,
+    q: float = 22.7,
+    trajectory: Coordinates = None,
+    axis: str = "all",
+) -> float:
+    """
+    Incoherent intermediate scattering function averaged over all particles and the
+    variance.
+    See isf_raw for details.
+    """
+    values = isf_raw(start_frame, end_frame, q=q, trajectory=trajectory, axis=axis)
+    return values.mean(), values.var()
+
+
 def rotational_autocorrelation(
     start_frame: CoordinateFrame, end_frame: CoordinateFrame, order: int = 2
 ) -> float:
@@ -430,6 +460,7 @@ def non_gaussian_parameter(
     end_frame: CoordinateFrame,
     trajectory: Coordinates = None,
     axis: str = "all",
+    full_output = False,
 ) -> float:
     r"""
     Calculate the non-Gaussian parameter.
@@ -442,27 +473,41 @@ def non_gaussian_parameter(
     else:
         vectors = displacements_without_drift(start_frame, end_frame, trajectory)
     if axis == "all":
-        r = (vectors**2).sum(axis=1)
+        r2 = (vectors**2).sum(axis=1)
         dimensions = 3
     elif axis == "xy" or axis == "yx":
-        r = (vectors[:, [0, 1]]**2).sum(axis=1)
+        r2 = (vectors[:, [0, 1]]**2).sum(axis=1)
         dimensions = 2
     elif axis == "xz" or axis == "zx":
-        r = (vectors[:, [0, 2]]**2).sum(axis=1)
+        r2 = (vectors[:, [0, 2]]**2).sum(axis=1)
         dimensions = 2
     elif axis == "yz" or axis == "zy":
-        r = (vectors[:, [1, 2]]**2).sum(axis=1)
+        r2 = (vectors[:, [1, 2]]**2).sum(axis=1)
         dimensions = 2
     elif axis == "x":
-        r = vectors[:, 0] ** 2
+        r2 = vectors[:, 0] ** 2
         dimensions = 1
     elif axis == "y":
-        r = vectors[:, 1] ** 2
+        r2 = vectors[:, 1] ** 2
         dimensions = 1
     elif axis == "z":
-        r = vectors[:, 2] ** 2
+        r2 = vectors[:, 2] ** 2
         dimensions = 1
     else:
         raise ValueError('Parameter axis has to be ether "all", "x", "y", or "z"!')
+    
+    m2 = np.mean(r2)
+    m4 = np.mean(r2**2)
+    if m2 == 0.0:
+        if full_output:
+            return 0.0, 0.0, 0.0
+        else:
+            return 0.0
+
+    alpha_2 = (m4 / ((1 + 2 / dimensions) * m2**2)) - 1
+    if full_output:
+        return alpha_2, m2, m4
+    else:
+        return alpha_2
+
 
-    return (np.mean(r**2) / ((1 + 2 / dimensions) * (np.mean(r) ** 2))) - 1

src/mdevaluate/utils.py

@@ -357,6 +357,37 @@ def quick1etau(t: ArrayLike, C: ArrayLike, n: int = 7) -> float:
     return tau_est
 
 
+def quicknongaussfit(t, C, width=2):
+    """
+    Estimates the time and height of the peak in the non-Gaussian function.
+    C is C(t) the correlation function
+    """
+    def ffunc(t,y0,A_main,log_tau_main,sig_main):
+        main_peak = A_main*np.exp(-(t - log_tau_main)**2 / (2 * sig_main**2))
+        return y0 + main_peak
+    
+    # first rough estimate, the closest time. This is returned if the interpolation fails!
+    tau_est = t[np.argmax(C)]
+    nG_max = np.amax(C)
+    try:
+        with np.errstate(invalid='ignore'):
+            corr = C[t > 0]
+            time = np.log10(t[t > 0])
+            tau = time[np.argmax(corr)]
+            mask = (time>tau-width/2) & (time<tau+width/2)
+            time = time[mask] ; corr = corr[mask]
+            nG_min = C[t > 0].min()
+            guess = [nG_min, nG_max-nG_min, tau, 0.6]
+            popt = curve_fit(ffunc, time, corr, p0=guess, maxfev=10000)[0]
+            tau_est = 10**popt[-2]
+            nG_max = popt[0] + popt[1]
+    except:
+        pass
+    if np.isnan(tau_est):
+        tau_est = np.inf
+    return tau_est, nG_max
+
+
 def susceptibility(
     time: NDArray, correlation: NDArray, **kwargs
 ) -> tuple[NDArray, NDArray]: