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DOUBLE PRECISION FUNCTION DAPOLY(N,P)
C
C CALCULATES AREA OF A POLYGON DESCRIBED BY N POINTS (P)
C ( N .LE. 10 )
C
C AREA= -1* LINE INTEGRAL OF Y*DX
C
C AREA CONTRIBUTION FROM SIDE WHOSE ENDS ARE P(I), P(J):
C A(I,J)= 0.5 * (Y(I)+Y(J)) * (X(I)-X(J))
C
DOUBLE PRECISION P(2,1)
INTEGER KEDGE(2,10), K(2,10)
C
DATA KEDGE/ 1,2, 2,3, 3,4, 4,5, 5,6, 6,7, 7,8, 8,9, 9,10,
1 10,1/
C
DO 10 I=1,2
DO 10 J=1,N
10 K(I,J)= KEDGE(I,J)
K(2,N)= 1
DAPOLY= 0.0
C
DO 20 NN= 1,N
K1= K(1,NN)
K2= K(2,NN)
20 DAPOLY= DAPOLY +5.D-1 * (P(2,K1)+P(2,K2)) * (P(1,K1)-P(1,K2))
RETURN
END
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