diff --git a/lib/matplotlib/scale.py b/lib/matplotlib/scale.py
index a55e375c171f..dc22a0877859 100644
--- a/lib/matplotlib/scale.py
+++ b/lib/matplotlib/scale.py
@@ -372,60 +372,39 @@ def get_transform(self):
class SymmetricalLogTransform(Transform):
input_dims = output_dims = 1
- def __init__(self, base, linthresh, linscale):
+ def __init__(self, base, linthresh):
Transform.__init__(self)
if base <= 1.0:
raise ValueError("'base' must be larger than 1")
if linthresh <= 0.0:
raise ValueError("'linthresh' must be positive")
- if linscale <= 0.0:
- raise ValueError("'linscale' must be positive")
self.base = base
self.linthresh = linthresh
- self.linscale = linscale
- self._linscale_adj = (linscale / (1.0 - self.base ** -1))
self._log_base = np.log(base)
def transform_non_affine(self, a):
- abs_a = np.abs(a)
- with np.errstate(divide="ignore", invalid="ignore"):
- out = np.sign(a) * self.linthresh * (
- self._linscale_adj +
- np.log(abs_a / self.linthresh) / self._log_base)
- inside = abs_a <= self.linthresh
- out[inside] = a[inside] * self._linscale_adj
- return out
+ return np.arcsinh(a / 2 / self.linthresh) / self._log_base
def inverted(self):
- return InvertedSymmetricalLogTransform(self.base, self.linthresh,
- self.linscale)
+ return InvertedSymmetricalLogTransform(self.base, self.linthresh)
class InvertedSymmetricalLogTransform(Transform):
input_dims = output_dims = 1
- def __init__(self, base, linthresh, linscale):
+ def __init__(self, base, linthresh):
Transform.__init__(self)
- symlog = SymmetricalLogTransform(base, linthresh, linscale)
+ symlog = SymmetricalLogTransform(base, linthresh)
self.base = base
self.linthresh = linthresh
self.invlinthresh = symlog.transform(linthresh)
- self.linscale = linscale
- self._linscale_adj = (linscale / (1.0 - self.base ** -1))
+ self._log_base = np.log(base)
def transform_non_affine(self, a):
- abs_a = np.abs(a)
- with np.errstate(divide="ignore", invalid="ignore"):
- out = np.sign(a) * self.linthresh * (
- np.power(self.base,
- abs_a / self.linthresh - self._linscale_adj))
- inside = abs_a <= self.invlinthresh
- out[inside] = a[inside] / self._linscale_adj
- return out
+ return np.sinh(a * self._log_base) * 2 * self.linthresh
def inverted(self):
- return SymmetricalLogTransform(self.base,
- self.linthresh, self.linscale)
+ return SymmetricalLogTransform(self.base, self.linthresh)
class SymmetricalLogScale(ScaleBase):
@@ -434,31 +413,29 @@ class SymmetricalLogScale(ScaleBase):
positive and negative directions from the origin.
Since the values close to zero tend toward infinity, there is a
- need to have a range around zero that is linear. The parameter
- *linthresh* allows the user to specify the size of this range
- (-*linthresh*, *linthresh*).
+ need to have a range around zero that is approximately linear.
+ The parameter *linthresh* allows the user to specify where the transition
+ from log scaling to linear scaling should take place with the linear scale
+ being the region (-*linthresh*, *linthresh*).
+
+ The mathematical transform is defined to be the hyperbolic arcsin
+ `f(x) = arcsinh(x/2) = ln(x/2 + sqrt(x/2 + 1))` which has a well-defined
+ inverse and is valid over the entire real number line.
Parameters
----------
base : float, default: 10
The base of the logarithm.
- linthresh : float, default: 2
- Defines the range ``(-x, x)``, within which the plot is linear.
+ linthresh : float, default: 1
+ Defines the range ``(-x, x)``, within which the plot is
+ approximately linear.
This avoids having the plot go to infinity around zero.
subs : sequence of int
Where to place the subticks between each major tick.
For example, in a log10 scale: ``[2, 3, 4, 5, 6, 7, 8, 9]`` will place
8 logarithmically spaced minor ticks between each major tick.
-
- linscale : float, optional
- This allows the linear range ``(-linthresh, 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.
"""
name = 'symlog'
@@ -479,8 +456,7 @@ def __init__(self, axis, **kwargs):
@cbook._rename_parameter("3.3", f"base{axis_name}", "base")
@cbook._rename_parameter("3.3", f"linthresh{axis_name}", "linthresh")
@cbook._rename_parameter("3.3", f"subs{axis_name}", "subs")
- @cbook._rename_parameter("3.3", f"linscale{axis_name}", "linscale")
- def __init__(*, base=10, linthresh=2, subs=None, linscale=1, **kwargs):
+ def __init__(*, base=10, linthresh=1, subs=None, **kwargs):
if kwargs:
warn_deprecated(
"3.2.0",
@@ -489,15 +465,14 @@ def __init__(*, base=10, linthresh=2, subs=None, linscale=1, **kwargs):
f"argument {next(iter(kwargs))!r}; in the future, "
f"this will raise a TypeError")
)
- return base, linthresh, subs, linscale
+ return base, linthresh, subs
- base, linthresh, subs, linscale = __init__(**kwargs)
- self._transform = SymmetricalLogTransform(base, linthresh, linscale)
+ base, linthresh, subs = __init__(**kwargs)
+ self._transform = SymmetricalLogTransform(base, linthresh)
self.subs = subs
base = property(lambda self: self._transform.base)
linthresh = property(lambda self: self._transform.linthresh)
- linscale = property(lambda self: self._transform.linscale)
def set_default_locators_and_formatters(self, axis):
# docstring inherited
diff --git a/lib/matplotlib/tests/test_scale.py b/lib/matplotlib/tests/test_scale.py
index c9bed31ab4f9..bf2f5a20f9ed 100644
--- a/lib/matplotlib/tests/test_scale.py
+++ b/lib/matplotlib/tests/test_scale.py
@@ -27,7 +27,7 @@ def test_log_scales(fig_test, fig_ref):
def test_symlog_mask_nan():
# Use a transform round-trip to verify that the forward and inverse
# transforms work, and that they respect nans and/or masking.
- slt = SymmetricalLogTransform(10, 2, 1)
+ slt = SymmetricalLogTransform(10, 2)
slti = slt.inverted()
x = np.arange(-1.5, 5, 0.5)
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