SetDefaultDashedStyle — Sets the on/off pattern for dashed lines.
$plot->SetDefaultDashedStyle($style)
SetDefaultDashedStyle sets the line style for dashed
lines. That is, it customizes the look of dashed lines by specifying the
dash and gap lengths.
$styleA string specifying the number of alternating colored and transparent dots, in order. For example, '4-3' means 4 colored, 3 transparent; '2-3-1-2' means 2 colored, 3 transparent, 1 colored, 2 transparent.
The default dashed style is '2-4', meaning 2 pixels drawn, followed by a gap of 4 pixels.
All dashed lines on a plot must use the same dashed style. Dashed lines are used for the grid (unless disabled with SetDrawDashedGrid), and for any data sets with line style set to dashed with SetLineStyles.