[Bug] smoothMonotone generates saddle points

[akloeckner]

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 help

Any 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.

See home-assistant/frontend#29907 (comment)