Document SymmetricalLogLocator parameters.

anntzer · anntzer · commit aba2973a3500 · 2020-01-27T07:31:52.000+01:00
I didn't want to duplicate all the math explained in
SymmetricalLogScale, just to point out the (awkward) interaction between
*transform* and *base*/*linthresh*.  (Probably one should deprecate
*transform* and make the Locator behave more like LogLocator...)
diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -2499,11 +2499,28 @@ def nonsingular(self, vmin, vmax):
 
 class SymmetricalLogLocator(Locator):
     """
-    Determine the tick locations for symmetric log axes
+    Determine the tick locations for symmetric log axes.
     """
 
     def __init__(self, transform=None, subs=None, linthresh=None, base=None):
-        """Place ticks on the locations ``base**i*subs[j]``."""
+        """
+        Parameters
+        ----------
+        transform : `~.scale.SymmetricalLogTransform`, optional
+            If set, defines the *base* and *linthresh* of the symlog transform.
+        base, linthresh : float, optional
+            The *base* and *linthresh* of the symlog transform, as documented
+            for `.SymmetricalLogScale`.  These parameters are only used if
+            *transform* is not set.
+        subs : sequence of float, default: [1]
+            The multiples of integer powers of the base where ticks are placed,
+            i.e., ticks are placed at
+            ``[sub * base**i for i in ... for sub in subs]``.
+
+        Notes
+        -----
+        Either *transform*, or both *base* and *linthresh*, must be given.
+        """
         if transform is not None:
             self._base = transform.base
             self._linthresh = transform.linthresh
