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ticker.LinearLocator view_limits algorithm improvement closes #6142 #6146

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Merged
merged 1 commit into from
May 4, 2016
Merged

ticker.LinearLocator view_limits algorithm improvement closes #6142 #6146

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16 changes: 16 additions & 0 deletions doc/api/api_changes/2015-03-14-SSH.rst
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@@ -0,0 +1,16 @@
``matplotlib.ticker.LinearLocator`` algorithm update
```````````````````````````

The ``matplotlib.ticker.LinearLocator`` is used to define the range and location
of tickmarks of a plot when the user wants a exact number of ticks.
``LinearLocator`` thus differs from the default locator ``MaxNLocator``, which
does not necessarily return the exact user requested number of ticks.

The view range algorithm in ``matplotlib.ticker.LinearLocator`` has been
changed so that more convenient tick location are chosen. The new algorithm
returns a plot view range that is a multiple of the user requested number of
ticks. This ensures tick marks to be located at whole integers more
constistently. For example, when both y-axis of a``twinx`` plot use
``matplotlib.ticker.LinearLocator`` with the same number of ticks, the grids of
both axis will be properly aligned at convenient tick locations.

3 changes: 2 additions & 1 deletion lib/matplotlib/axes/_base.py
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Expand Up @@ -3780,7 +3780,8 @@ def twinx(self):
create a twin of Axes for generating a plot with a sharex
x-axis but independent y axis. The y-axis of self will have
ticks on left and the returned axes will have ticks on the
right.
right. To ensure tick marks of both axis align, see
:class:`~matplotlib.ticker.LinearLocator`

.. note::
For those who are 'picking' artists while using twinx, pick
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5 changes: 3 additions & 2 deletions lib/matplotlib/ticker.py
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Expand Up @@ -1231,10 +1231,11 @@ def view_limits(self, vmin, vmax):
vmax += 1

if rcParams['axes.autolimit_mode'] == 'round_numbers':
exponent, remainder = _divmod(math.log10(vmax - vmin), 1)
exponent, remainder = _divmod(math.log10(vmax - vmin),
math.log10(max([self.numticks-1, 1])))
if remainder < 0.5:
exponent -= 1
scale = 10 ** (-exponent)
scale = max([self.numticks-1, 1]) ** (-exponent)
vmin = math.floor(scale * vmin) / scale
vmax = math.ceil(scale * vmax) / scale

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