Hi Tarik @tgouhier,

I have a question regarding the arrow() function.
Currently, the function generates a polygon representing the arrow. There are two parameters to control the size of the arrow - width and length.

I think it would be better to print an arrow using the text() function as a character at specified coordinates. This would allow users to use different arrow shapes.

Take a look at my implementation here - arrow2() function:
https://github.com/tgouhier/biwavelet/blob/master/R/phase.plot.R

Notice that my function uses just a single size parameter.

Here are some examples how it might look like when using arrow2 instead of arrow: