What error are you getting? (perhaps you need "save carre,p,a,b,c,d,N,P,M ;")
A perpendicular line is also the line "rotated 90" (about the intersection point). Alan On Sun, 26 Jan 2020 00:09:38 +0100 Fabrice Couvreur <fabrice1.couvr...@gmail.com> wrote: > Hi, > The point M is such that the line (CM) is perpendicular to the line (NP). > I do not understand the error of this code. > Thank you > Fabrice > > \usecolors[xwi] > \starttext > \startMPcode > path carre, p; > carre = unitsquare scaled 138; > > pair a, b, c, d, N, P, M; > a = point 0 of carre; > b = point 1 of carre; > c = point 2 of carre; > d = point 3 of carre; > > p = b -- d; > N = whatever[a,d]; > P = whatever[a,b]; > M = whatever[b,d]; > (M - c) dotprod (P - N) = 0; > > draw M -- c; > > draw p withcolor \MPcolor{navy}; > draw carre withcolor \MPcolor{firebrick}; > > label.lft("$A$", point 0 of carre); > label.lrt("$B$", point 1 of carre); > label.urt("$C$", point 2 of carre); > label.ulft("$D$", point 3 of carre); > \stopMPcode > \stoptext ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki! maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context webpage : http://www.pragma-ade.nl / http://context.aanhet.net archive : https://bitbucket.org/phg/context-mirror/commits/ wiki : http://contextgarden.net ___________________________________________________________________________________