[NTG-context] A question about whatever (Metapost)

[Alan Braslau]

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.couvreur at 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