Fix plot crash on negative errors

Framework/PythonInterface/mantid/plots/axesfunctions.py

@@ -41,6 +41,7 @@
 )
 from mantid.plots.utility import MantidAxType
 from mantid.plots.quad_mesh_wrapper import QuadMeshWrapper
+from mantid import logger
 
 # Used for initializing searches of max, min values
 _LARGEST, _SMALLEST = float(sys.maxsize), -sys.maxsize
@@ -286,6 +287,14 @@ def errorbar(axes, workspace, *args, **kwargs):
         _setLabels1D(axes, workspace, indices, normalize_by_bin_width=normalize_by_bin_width, axis=axis)
     kwargs.pop("normalize_by_bin_width", None)
 
+    if dy is not None and min(dy) < 0:
+        dy = None
+        logger.warning("Negative values found in y error when plotting error bars. Continuing without y error bars.")
+
+    if dx is not None and min(dx) < 0:
+        dx = None
+        logger.warning("Negative values found in x error when plotting error bars. Continuing without x error bars.")
+
     return axes.errorbar(x, y, dy, dx, *args, **kwargs)
 
 

Framework/PythonInterface/test/python/mantid/plots/axesfunctionsTest.py

@@ -45,6 +45,12 @@ def setUpClass(cls):
             VerticalAxisValues=[4, 6, 8],
             OutputWorkspace="ws2d_histo",
         )
+        cls.ws2d_histo_negative_errors = CreateWorkspace(
+            DataX=[1, 2, 3, 4],
+            DataY=[10, 20, 30, 40],
+            DataE=[1, -2, 3, -4],
+            OutputWorkspace="ws2d_histo_negative_errors"
+        )
         cls.ws2d_histo_non_dist = CreateWorkspace(
             DataX=[10, 20, 30, 10, 20, 30],
             DataY=[2, 3, 4, 5],
@@ -151,6 +157,10 @@ def test_1d_errorbars(self):
         funcs.errorbar(ax, self.ws2d_histo, specNum=2, linewidth=6)
         funcs.errorbar(ax, self.ws_MD_1d, "bo")
 
+    def test_1d_errorbars_with_negative_errors(self):
+        _, ax = plt.subplots()
+        funcs.errorbar(ax, self.ws2d_histo_negative_errors, specNum=1)
+
     def test_1d_scatter(self):
         fig, ax = plt.subplots()
         funcs.scatter(ax, self.ws2d_histo, specNum=1)

docs/source/release/v6.11.0/Workbench/Bugfixes/37973.rst

@@ -0,0 +1 @@
+- Fixed crash when attempting to plot data with negative error values.