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MODULE convexity
  TYPE point
    COMPLEX::z
  END TYPE point
CONTAINS
  FUNCTION orientation(p,i) RESULT(orient)
  TYPE(point),DIMENSION(:),INTENT(in)::p
  INTEGER::i,n
  REAL::orient,f
  COMPLEX::z1,z2,z3
  f(z1,z2,z3)=REAL(z2-z1)*AIMAG(z3-z2)-REAL(z3-z2)*AIMAG(z2-z1)
  n=SIZE(p)
  IF(i==n-1)THEN
     orient=f(p(n-1).z,p(n).z,p(1).z)
  ELSE IF(i==n)THEN
     orient=f(p(n).z,p(1).z,p(2).z)
  ELSE
     orient=f(p(i).z,p(i+1).z,p(i+2).z)
  END IF
  END FUNCTION orientation
  !
   SUBROUTINE convex_polygon(p,convex)
   LOGICAL::convex
   TYPE(point),DIMENSION(:),INTENT(in)::p
   INTEGER::i,n,anticlockwise
   convex=.TRUE.;n=SIZE(P)
   IF(orientation(p,1)>0)THEN
      anticlockwise=1
   ELSE
      anticlocakwise=-1
   END IF
   DO i=2,n
       IF(anticlockwise*orientation(p,i)<0)THEN
           convex=.FALSE.;EXIT
           END IF
           END DO
           END SUBROUTINE convex_polygon
   END MODULE convexity
!
   PROGRAM test
   USE convexity
   INTEGER,parameter::n=6
   TYPE(point),DIMENSION(1:n)::polygon
   LOGICAL::convex
   INTEGER::i
   OPEN(1,FILE='convex')
   DO I=1,2
    READ(1,*)polygon
        CALL convex_polygon(polygon,convex)
        IF(convex==.TRUE.)PRINT*,'polygon is convex'
        IF(convex/=.TRUE.)PRINT*,'polygon is not convex'
   END DO
   END PROGRAM test

Originally posted by janecool at 2010-08-29 10:03:47:
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Originally posted by zyj8119 at 2010-08-29 10:09:13:

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Originally posted by zyj8119 at 2010-08-29 10:09:13:

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