@@ -861,20 +861,23 @@ class LogFormatter(Formatter):
861861
862862 labelOnlyBase : bool, default: False
863863 If True, label ticks only at integer powers of base.
864- This is normally True for major ticks and False for
865- minor ticks.
864+ This is normally True for major ticks and False for minor ticks.
866865
867866 minor_thresholds : (subset, all), default: (1, 0.4)
868867 If labelOnlyBase is False, these two numbers control
869868 the labeling of ticks that are not at integer powers of
870- base; normally these are the minor ticks. The controlling
871- parameter is the log of the axis data range. In the typical
872- case where base is 10 it is the number of decades spanned
873- by the axis, so we can call it 'numdec'. If ``numdec <= all``,
874- all minor ticks will be labeled. If ``all < numdec <= subset``,
875- then only a subset of minor ticks will be labeled, so as to
876- avoid crowding. If ``numdec > subset`` then no minor ticks will
877- be labeled.
869+ base; normally these are the minor ticks.
870+
871+ The first number (*subset*) is the largest number of major ticks for
872+ which minor ticks are labeled; e.g., the default, 1, means that minor
873+ ticks are labeled as long as there is no more than 1 major tick. (It
874+ is assumed that major ticks are at integer powers of *base*.)
875+
876+ The second number (*all*) is a threshold, in log-units of the axis
877+ limit range, over which only a subset of the minor ticks are labeled,
878+ so as to avoid crowding; e.g., with the default value (0.4) and the
879+ usual ``base=10``, all minor ticks are shown only if the axis limit
880+ range spans less than 0.4 decades.
878881
879882 linthresh : None or float, default: None
880883 If a symmetric log scale is in use, its ``linthresh``
@@ -898,12 +901,9 @@ class LogFormatter(Formatter):
898901
899902 Examples
900903 --------
901- To label a subset of minor ticks when the view limits span up
902- to 2 decades, and all of the ticks when zoomed in to 0.5 decades
903- or less, use ``minor_thresholds=(2, 0.5)``.
904-
905- To label all minor ticks when the view limits span up to 1.5
906- decades, use ``minor_thresholds=(1.5, 1.5)``.
904+ To label a subset of minor ticks when there are up to 2 major ticks,
905+ and all of the ticks when zoomed in to 0.5 decades or less, use
906+ ``minor_thresholds=(2, 0.5)``.
907907 """
908908
909909 def __init__ (self , base = 10.0 , labelOnlyBase = False ,
@@ -971,22 +971,32 @@ def set_locs(self, locs=None):
971971 return
972972
973973 b = self ._base
974+ 974975 if linthresh is not None : # symlog
975- # Only compute the number of decades in the logarithmic part of the
976- # axis
977- numdec = 0
976+ # Only count ticks and decades in the logarithmic part of the axis.
977+ numdec = numticks = 0
978978 if vmin < - linthresh :
979979 rhs = min (vmax , - linthresh )
980- numdec += math .log (vmin / rhs ) / math .log (b )
980+ numticks += (
981+ math .floor (math .log (abs (rhs ), b ))
982+ - math .floor (math .nextafter (math .log (abs (vmin ), b ), - math .inf )))
983+ numdec += math .log (vmin / rhs , b )
981984 if vmax > linthresh :
982985 lhs = max (vmin , linthresh )
983- numdec += math .log (vmax / lhs ) / math .log (b )
986+ numticks += (
987+ math .floor (math .log (vmax , b ))
988+ - math .floor (math .nextafter (math .log (lhs , b ), - math .inf )))
989+ numdec += math .log (vmax / lhs , b )
984990 else :
985- vmin = math .log (vmin ) / math .log (b )
986- vmax = math .log (vmax ) / math .log (b )
987- numdec = abs (vmax - vmin )
988- 989- if numdec > self .minor_thresholds [0 ]:
991+ lmin = math .log (vmin , b )
992+ lmax = math .log (vmax , b )
993+ # The nextafter call handles the case where vmin is exactly at a
994+ # decade (e.g. there's one major tick between 1 and 5).
995+ numticks = (math .floor (lmax )
996+ - math .floor (math .nextafter (lmin , - math .inf )))
997+ numdec = abs (lmax - lmin )
998+ 999+ if numticks > self .minor_thresholds [0 ]:
9901000 # Label only bases
9911001 self ._sublabels = {1 }
9921002 elif numdec > self .minor_thresholds [1 ]:
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