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SUBROUTINE RAND3 (F,S,Q,N)
C
C COMPUTES MEAN RESPONSE Q
C
INTEGER CHECK ,NAME(2)
REAL Q(2) ,F(1) ,S(1)
COMMON /CONDAS/ PHI ,TWOPI ,RADEG ,DEGRA ,
1 S4PISQ
DATA NAME / 4HRAND ,4H3 /
C
C F IS ARRAY OF FREQUENCIES
C S IS ARRAY OF POWER SPECTRAL DENSITY FUNCTIONS
C Q IS MEAN RESPONSE
C N IS NUMBER OF FREQUENCIES
C
SUM1 = 0.0
NN = N - 1
SUM = 0.0
DO 10 I = 1,NN
DF = F(I+1) - F(I)
SUM = SUM + (S(I)+S(I+1))*DF
FI = F(I )*F(I )
FI1 = F(I+1 )*F(I+1)
FII1 = 2.*F(I)*F(I+1)
ALP = (3.*FI+FII1+FI1)/6.
BTA = (FI+FII1+3.*FI1)/6.
SUM1 = SUM1 + (ALP*S(I)+BTA*S(I+1))*DF
10 CONTINUE
SUM = SQRT(SUM*0.5)
SUM1 = SQRT(SUM1*.5)
Q(1) = SUM
Q(2) = 0.0
Q1 = Q(1)
IF (Q1 .NE. 0.0) Q(2) = SUM1/Q1
CHECK= 123456789
RETURN
C
C AUTOCORRALATION FUNCTION
C
ENTRY RAND4 (F,S,TAU,R,N)
C =========================
C
C COMPUTES AUTOCORRALATION FUNCTION R AT TIME TAU
C WHERE F,S AS ABOVE. IF TAU = 0.0 R = Q*Q
C
IF (CHECK .NE. 123456789) CALL MESAGE (-37,0,NAME)
IF (TAU .EQ. 0.0) GO TO 30
NN = N - 1
A = 2.0*PHI*TAU
B = 1.0/A
SUM = 0.0
DO 20 I = 1,NN
SUM = SUM + B*(S(I+1)-S(I))/(F(I+1)-F(I))*(COS(A*F(I+1))
1 - COS(A*F(I))) + S(I+1)*SIN(A*F(I+1))-S(I)*SIN(A*F(I))
20 CONTINUE
SUM = SUM*B
R = SUM
GO TO 40
30 R = Q1*Q1
40 RETURN
END
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