diff --git a/doc/api/next_api_changes/behaviour.rst b/doc/api/next_api_changes/behaviour.rst
index be394fbd4277..3cca24e94df7 100644
--- a/doc/api/next_api_changes/behaviour.rst
+++ b/doc/api/next_api_changes/behaviour.rst
@@ -85,3 +85,11 @@ Previously, rcParams entries whose values were color-like accepted "spurious"
extra letters or characters in the "middle" of the string, e.g. ``"(0, 1a, '0.5')"``
would be interpreted as ``(0, 1, 0.5)``. These extra characters (including the
internal quotes) now cause a ValueError to be raised.
+
+`.SymLogNorm` now has a *base* parameter
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Previously, `.SymLogNorm` had no *base* kwarg, and defaulted to ``base=np.e``
+whereas the documentation said it was ``base=10``. In preparation to make
+the default 10, calling `.SymLogNorm` without the new *base* kwarg emits a
+deprecation warning.
diff --git a/examples/userdemo/colormap_normalizations.py b/examples/userdemo/colormap_normalizations.py
index 419a4b5051aa..2844fd9f9646 100644
--- a/examples/userdemo/colormap_normalizations.py
+++ b/examples/userdemo/colormap_normalizations.py
@@ -69,7 +69,7 @@
pcm = ax[0].pcolormesh(X, Y, Z1,
norm=colors.SymLogNorm(linthresh=0.03, linscale=0.03,
- vmin=-1.0, vmax=1.0),
+ vmin=-1.0, vmax=1.0, base=10),
cmap='RdBu_r')
fig.colorbar(pcm, ax=ax[0], extend='both')
diff --git a/examples/userdemo/colormap_normalizations_symlognorm.py b/examples/userdemo/colormap_normalizations_symlognorm.py
index 780381e43da8..b0fbf0dc30ea 100644
--- a/examples/userdemo/colormap_normalizations_symlognorm.py
+++ b/examples/userdemo/colormap_normalizations_symlognorm.py
@@ -29,7 +29,7 @@
pcm = ax[0].pcolormesh(X, Y, Z,
norm=colors.SymLogNorm(linthresh=0.03, linscale=0.03,
- vmin=-1.0, vmax=1.0),
+ vmin=-1.0, vmax=1.0, base=10),
cmap='RdBu_r')
fig.colorbar(pcm, ax=ax[0], extend='both')
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
index 52d2b2438959..5b584cfac2b3 100644
--- a/lib/matplotlib/colors.py
+++ b/lib/matplotlib/colors.py
@@ -1202,8 +1202,8 @@ class SymLogNorm(Normalize):
*linthresh* allows the user to specify the size of this range
(-*linthresh*, *linthresh*).
"""
- def __init__(self, linthresh, linscale=1.0,
- vmin=None, vmax=None, clip=False):
+ def __init__(self, linthresh, linscale=1.0, vmin=None, vmax=None,
+ clip=False, *, base=None):
"""
Parameters
----------
@@ -1213,14 +1213,29 @@ def __init__(self, linthresh, linscale=1.0,
linscale : float, default: 1
This allows the linear range (-*linthresh* to *linthresh*) to be
stretched relative to the logarithmic range. Its value is the
- number of decades to use for each half of the linear range. For
- example, when *linscale* == 1.0 (the default), the space used for
- the positive and negative halves of the linear range will be equal
- to one decade in the logarithmic range.
+ number of powers of *base* (decades for base 10) to use for each
+ half of the linear range. For example, when *linscale* == 1.0
+ (the default), the space used for the positive and negative halves
+ of the linear range will be equal to a decade in the logarithmic
+ range if ``base=10``.
+ base : float, default: None
+ For v3.2 the default is the old value of ``np.e``, but that is
+ deprecated for v3.3 when base will default to 10. During the
+ transition, specify the *base* kwarg to avoid a deprecation
+ warning.
"""
Normalize.__init__(self, vmin, vmax, clip)
+ if base is None:
+ self._base = np.e
+ cbook.warn_deprecated("3.3", message="default base will change "
+ "from np.e to 10. To suppress this warning specify the base "
+ "kwarg.")
+ else:
+ self._base = base
+ self._log_base = np.log(self._base)
+
self.linthresh = float(linthresh)
- self._linscale_adj = (linscale / (1.0 - np.e ** -1))
+ self._linscale_adj = (linscale / (1.0 - self._base ** -1))
if vmin is not None and vmax is not None:
self._transform_vmin_vmax()
@@ -1255,7 +1270,8 @@ def _transform(self, a):
with np.errstate(invalid="ignore"):
masked = np.abs(a) > self.linthresh
sign = np.sign(a[masked])
- log = (self._linscale_adj + np.log(np.abs(a[masked]) / self.linthresh))
+ log = (self._linscale_adj +
+ np.log(np.abs(a[masked]) / self.linthresh) / self._log_base)
log *= sign * self.linthresh
a[masked] = log
a[~masked] *= self._linscale_adj
@@ -1265,7 +1281,8 @@ def _inv_transform(self, a):
"""Inverse inplace Transformation."""
masked = np.abs(a) > (self.linthresh * self._linscale_adj)
sign = np.sign(a[masked])
- exp = np.exp(sign * a[masked] / self.linthresh - self._linscale_adj)
+ exp = np.power(self._base,
+ sign * a[masked] / self.linthresh - self._linscale_adj)
exp *= sign * self.linthresh
a[masked] = exp
a[~masked] /= self._linscale_adj
diff --git a/lib/matplotlib/tests/test_colors.py b/lib/matplotlib/tests/test_colors.py
index 05a81e26def3..d1cedfeb141e 100644
--- a/lib/matplotlib/tests/test_colors.py
+++ b/lib/matplotlib/tests/test_colors.py
@@ -398,7 +398,7 @@ def test_SymLogNorm():
"""
Test SymLogNorm behavior
"""
- norm = mcolors.SymLogNorm(3, vmax=5, linscale=1.2)
+ norm = mcolors.SymLogNorm(3, vmax=5, linscale=1.2, base=np.e)
vals = np.array([-30, -1, 2, 6], dtype=float)
normed_vals = norm(vals)
expected = [0., 0.53980074, 0.826991, 1.02758204]
@@ -408,16 +408,30 @@ def test_SymLogNorm():
_mask_tester(norm, vals)
# Ensure that specifying vmin returns the same result as above
- norm = mcolors.SymLogNorm(3, vmin=-30, vmax=5, linscale=1.2)
+ norm = mcolors.SymLogNorm(3, vmin=-30, vmax=5, linscale=1.2, base=np.e)
normed_vals = norm(vals)
assert_array_almost_equal(normed_vals, expected)
+ # test something more easily checked.
+ norm = mcolors.SymLogNorm(1, vmin=-np.e**3, vmax=np.e**3, base=np.e)
+ nn = norm([-np.e**3, -np.e**2, -np.e**1, -1,
+ 0, 1, np.e**1, np.e**2, np.e**3])
+ xx = np.array([0., 0.109123, 0.218246, 0.32737, 0.5, 0.67263,
+ 0.781754, 0.890877, 1.])
+ assert_array_almost_equal(nn, xx)
+ norm = mcolors.SymLogNorm(1, vmin=-10**3, vmax=10**3, base=10)
+ nn = norm([-10**3, -10**2, -10**1, -1,
+ 0, 1, 10**1, 10**2, 10**3])
+ xx = np.array([0., 0.121622, 0.243243, 0.364865, 0.5, 0.635135,
+ 0.756757, 0.878378, 1.])
+ assert_array_almost_equal(nn, xx)
+
def test_SymLogNorm_colorbar():
"""
Test un-called SymLogNorm in a colorbar.
"""
- norm = mcolors.SymLogNorm(0.1, vmin=-1, vmax=1, linscale=1)
+ norm = mcolors.SymLogNorm(0.1, vmin=-1, vmax=1, linscale=1, base=np.e)
fig = plt.figure()
mcolorbar.ColorbarBase(fig.add_subplot(111), norm=norm)
plt.close(fig)
@@ -428,7 +442,7 @@ def test_SymLogNorm_single_zero():
Test SymLogNorm to ensure it is not adding sub-ticks to zero label
"""
fig = plt.figure()
- norm = mcolors.SymLogNorm(1e-5, vmin=-1, vmax=1)
+ norm = mcolors.SymLogNorm(1e-5, vmin=-1, vmax=1, base=np.e)
cbar = mcolorbar.ColorbarBase(fig.add_subplot(111), norm=norm)
ticks = cbar.get_ticks()
assert sum(ticks == 0) == 1
@@ -905,9 +919,10 @@ def __add__(self, other):
mydata = data.view(MyArray)
for norm in [mcolors.Normalize(), mcolors.LogNorm(),
- mcolors.SymLogNorm(3, vmax=5, linscale=1),
+ mcolors.SymLogNorm(3, vmax=5, linscale=1, base=np.e),
mcolors.Normalize(vmin=mydata.min(), vmax=mydata.max()),
- mcolors.SymLogNorm(3, vmin=mydata.min(), vmax=mydata.max()),
+ mcolors.SymLogNorm(3, vmin=mydata.min(), vmax=mydata.max(),
+ base=np.e),
mcolors.PowerNorm(1)]:
assert_array_equal(norm(mydata), norm(data))
fig, ax = plt.subplots()
diff --git a/tutorials/colors/colormapnorms.py b/tutorials/colors/colormapnorms.py
index 412278ac45cb..ea982b243207 100644
--- a/tutorials/colors/colormapnorms.py
+++ b/tutorials/colors/colormapnorms.py
@@ -98,7 +98,7 @@
pcm = ax[0].pcolormesh(X, Y, Z,
norm=colors.SymLogNorm(linthresh=0.03, linscale=0.03,
- vmin=-1.0, vmax=1.0),
+ vmin=-1.0, vmax=1.0, base=10),
cmap='RdBu_r')
fig.colorbar(pcm, ax=ax[0], extend='both')
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