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[Bug] smoothMonotone generates saddle points #21532
Description
Version
current
Link to Minimal Reproduction
see below
Steps to Reproduce
Use the ECharts help here:
https://apache.github.io/echarts-handbook/en/how-to/chart-types/line/basic-line/
Select a few points and set smoothMonotone to x.
With smoothMonotone:
Without smoothMonotone:
Current Behavior
Setting the option generates saddle points at the actual data points.
Expected Behavior
The graph should not have saddle points but simply be monotone.
Environment
ECharts helpAny additional comments?
I found this when examining data shown in home assistant. The data was surprising to me until I realized it was actually a graphing artifact.
Activity
helgasoft commentedon Apr 6, 2026
apparently this 'saddle' effect comes from smooth, not smoothMonotone - Demo.
And is probably by design.
awtaylor commentedon Oct 19, 2026
I believe the horizontal tangent at each sample comes from
smoothMonotone: 'x'(the control points keep that sample's y). That part is the behavior added in #7158.smooth: truewithout it can still bow past the samples, but it does not flatten every knot.#21794 leaves
'x'and'y'as they are and addssmoothMonotone: 'monotoneX'for a monotone curve that does not put a saddle on every sample.