Function tangent_inner

code/geometry/circles.cpp:35–38

  Q.first = A + normalize(u, rA);
  Q.second = B + normalize(u, rB); }
void tangent_inner(C(A,rA), C(B,rB), PP(P), PP(Q)) {
  point ip = (rA*B + rB*A)/(rA+rB);
  assert(tangent(ip, A, rA, P.first, Q.first) == 2);
  assert(tangent(ip, B, rB, P.second, Q.second) == 2); }
pair<point,double> circumcircle(point a, point b, point c) {
  b -= a, c -= a;
  point p = perp(b*norm(c)-c*norm(b))/2.0/cross(b, c);