Hello guys I'm trying to understand this piece of code in order to write the same thing with Python

up=src-(Multiplier*atr)

upPlot1 = plot(up, style=plot.style_linebr, linewidth=2, color=color.green)
upPlot2 = plot(up[1], style=plot.style_linebr, linewidth=2, color=color.red)

up1 = nz(up[1],up)

This actually shows the following, and I'm tryining to understand why the purple line has that shape.

GBPJPY_2021-12-23_18-21-18.png