Merge pull request #24555 from parthpankajtiwary/symlog-warn

tacaswell · web-flow · commit 041d4e02e60e · 2022-11-28T09:41:45.000-05:00
ENH: Add warning for SymLogScale when values in linear scale range
diff --git a/lib/matplotlib/scale.py b/lib/matplotlib/scale.py
@@ -389,6 +389,11 @@ def __init__(self, base, linthresh, linscale):
 
     def transform_non_affine(self, a):
         abs_a = np.abs(a)
+        if (abs_a < self.linthresh).all():
+            _api.warn_external(
+                "All values for SymLogScale are below linthresh, making "
+                "it effectively linear. You likely should lower the value "
+                "of linthresh. ")
         with np.errstate(divide="ignore", invalid="ignore"):
             out = np.sign(a) * self.linthresh * (
                 np.power(self.base,
diff --git a/lib/matplotlib/tests/test_scale.py b/lib/matplotlib/tests/test_scale.py
@@ -55,6 +55,20 @@ def test_symlog_mask_nan():
     assert type(out) == type(x)
 
 
+def test_symlog_linthresh():
+    np.random.seed(19680801)
+    x = np.random.random(100)
+    y = np.random.random(100)
+
+    fig, ax = plt.subplots()
+    plt.plot(x, y, 'o')
+    ax.set_xscale('symlog')
+    ax.set_yscale('symlog')
+
+    with pytest.warns(UserWarning, match="All values .* of linthresh"):
+        fig.canvas.draw()
+
+
 @image_comparison(['logit_scales.png'], remove_text=True)
 def test_logit_scales():
     fig, ax = plt.subplots()
