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bugs - RegionIntersection fails for some values with polygons


Bug introduced in 10.1 and fixed in 10.3.0




I want to find the intersection (region) of 2 polygons. I use RegionInstersection but it only works for some sizes, for example, when c=.5 it gives the correct result, but with c=.4 it only finds a line as intersection.


Area[r3[.5]] works fine...


Area[r3[.4]] does not work...


What is wrong?


b = 15.0;
d = 4.0;
lbp = 40.0;
d1E = 2.;
l1E = 7.0;

d1D = d1E;
l1D = 5.0;

r1 = Polygon[{{0, 0}, {lbp/2 - l1D, 0}, {lbp/2, d1D}, {lbp/2, 
     d}, {-(lbp/2), d}, {-(lbp/2), d1E}, {-(lbp/2) + l1E, 0}}];
r2[c_] := Rectangle[{-1.1 lbp/2, -1.5}, {1.1 lbp/2, c}];
r3[c_] := RegionIntersection[r1, r2[c]];

Answer



This bug has been fixed as of Mathematica 10.3.


b = 15.0; d = 4.0; lbp = 40.0; d1E = 2.; l1E = 7.0; d1D = d1E; l1D = 5.0;

r1 = Polygon[{{0, 0}, {lbp/2 - l1D, 0}, {lbp/2, d1D}, {lbp/2, d}, 
              {-(lbp/2), d}, {-(lbp/2), d1E}, {-(lbp/2) + l1E, 0}}];
r2[c_] := Rectangle[{-1.1 lbp/2, -1.5}, {1.1 lbp/2, c}];
r3[c_] := RegionIntersection[r1, r2[c]];
{Area[r3[.5]], Area[r3[.4]]}

(* {14.75, 11.68} *)

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