traceaxes
4 setytkstep
2 setymkstep
ticks
ymarks
pi ymark
e xmark
.25 xsubtick
/ymarkstyle {brtext} def
[-3 -1 1 5] {ymark} apply

-3 -1.5 setorigine
bleu traceaxes noir
[(1/6) (-1/4) (2/3) (-3/4) (1)] trig_ymarks
setTimes
[(-1/4) (1/3) (-3/4) (1)] (a) 5 coeff_xmarks