[metapost] MetaFont: Unexpected behavior of intersections times
Boguslaw Jackowski
B_Jackowski at GUST.org.pl
Fri Apr 8 19:13:38 CEST 2011
Hello, Everybody,
Dan Luecking:
> I once had two semicircles that crossed
> (theoretically) at the midpoint of each, and MP said
> they did not cross.
The only situation I can fancy is related to the inequality:
(point t of p) transformed T <> point t of (p transformed T)
rather obvious in the realm of discrete geometry. Below an example:
% ===
path p,q; numeric a,t; pair s;
t=0.72302;
beginfig(100);
def T = scaled 100 enddef;
p:=(0,0){up}..{down}(1,0); q:=p shifted point t of p; p:=p T; q:=q T;
show q intersectiontimes p;
draw p withcolor blue;
draw q withcolor blue;
def T = scaled 100 rotated a shifted s enddef;
a=67.43527; s=(0.66753,0.5755);
p:=(0,0){up}..{down}(1,0); q:=p shifted point t of p; p:=p T; q:=q T;
show q intersectiontimes p;
draw p withcolor red;
draw q withcolor red;
endfig;
end.
% ===
Rounding errors cause that the curves p and q after the same shift
and rotation become ("infinitesimally") disjoint. But I'm not sure
whether Dan observed a situation of this kind.
Cheers -- Jacko
--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Bogus\l{}aw Jackowski: B_Jackowski at GUST.ORG.PL
----------------------------------------------------------------
Hofstadter's Law: It always takes longer than you expect, even
when you take into account Hofstadter's Law.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
More information about the metapost
mailing list