hello! the problem was that the triangles contained not only the nodes but also their domain number (inside or out side the object) so when I used only the nodes of the triangle it worked perfectely using:
(I meant by bad it generates parallelogram instead of triangles)
figure(1) trisurf(t(1:3,:),p(1,:),p(2,:),p(3,:));title('ploted using trisurf ')
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