Hi, I don't know where you found the code, but the answer to "What is (0, r) rotated (a *i) doing?" is that it takes the point (0,r) and rotates it a*i degrees. For your labeling problem, see the last example of section 2.9 of https://www.pragma-ade.com/general/manuals/metafun-p.pdf /Mikael PS Please do not cross post here and on stackexchange (at least not without telling). On Wed, Aug 28, 2024 at 11:12 AM Shiv Shankar Dayal wrote:

I think it works like (0, r) rotated (a) -- (0, r) rotated (a * 2) -- ... (0, r) rotated (a*20) -- cycle

Is my understanding correct? Also, how can I label these vertices in a for loop?

On Wed, Aug 28, 2024 at 2:25 PM Shiv Shankar Dayal wrote:

...

Hi,

Consider following code:

vardef polygon_with_side(expr n, s) = save a, b, r; numeric a, b, r; a * n = 360; a + 2b = 180; r = s * sind(b) / sind(a); for i = 0 upto n-1: (0, r) rotated (a * i) -- endfor cycle enddef;

beginfig(1); path p; p = polygon_with_side(21, 20); draw p; endfig; bye;

It draws a polygon with 21 sides with radius 20. I understand all of it except the for loop.

What is (0, r) rotated (a *i) doing?

-- Respect, Shiv Shankar Dayal

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Shiv Shankar Dayal schrieb am 28.08.2024 um 12:23:

...

I don't know where you found the code, but the answer to "What is (0, r) rotated (a *i) doing?" is that it takes the point (0,r) and rotates it a*i degrees.

I do not understand the concept of rotating a point. It is rotated with respect to what reference?

You rotate around a point with the x and y coordinates 0. The blue dot shows the point with the coordinates 0. The green dot is rotated around this point. \starttext \startMPcode drawdot (0,0) withpen pencircle scaled 5mm withcolor blue; draw fullsquare scaled (4cm) withcolor red; \stopMPcode \startMPcode drawdot (0,0) withpen pencircle scaled 5mm withcolor blue; drawdot (1.5cm,0) withpen pencircle scaled 5mm withcolor green; draw fullsquare scaled (4cm) withcolor red; \stopMPcode \startMPcode drawdot (0,0) withpen pencircle scaled 5mm withcolor blue; drawdot (1.5cm,0) rotated (30) withpen pencircle scaled 5mm withcolor green; draw fullsquare scaled (4cm) withcolor red; \stopMPcode \startMPcode drawdot (0,0) withpen pencircle scaled 5mm withcolor blue; drawdot (1.5cm,0) rotated (60) withpen pencircle scaled 5mm withcolor green; draw fullsquare scaled (4cm) withcolor red; \stopMPcode \startMPcode drawdot (0,0) withpen pencircle scaled 5mm withcolor blue; drawdot (1.5cm,0) rotated (90) withpen pencircle scaled 5mm withcolor green; draw fullsquare scaled (4cm) withcolor red; \stopMPcode \stoptext Wolfgang