Fixed isf for 2d case

src/mdevaluate/correlation.py

@@ -219,13 +219,13 @@ def isf(
         return np.sinc(distance * q / np.pi).mean()
     elif axis == "xy" or axis == "yx":
         distance = (displacements[:, [0, 1]]**2).sum(axis=1) ** 0.5
-        return np.real(jn(0, distance * q / np.pi)).mean()
+        return np.real(jn(0, distance * q)).mean()
     elif axis == "xz" or axis == "zx":
         distance = (displacements[:, [0, 2]]**2).sum(axis=1) ** 0.5
-        return np.real(jn(0, distance * q / np.pi)).mean()
+        return np.real(jn(0, distance * q)).mean()
     elif axis == "yz" or axis == "zy":
         distance = (displacements[:, [1, 2]]**2).sum(axis=1) ** 0.5
-        return np.real(jn(0, distance * q / np.pi)).mean()
+        return np.real(jn(0, distance * q)).mean()
     elif axis == "x":
         distance = np.abs(displacements[:, 0])
         return np.mean(np.cos(np.abs(q * distance)))