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67 lines
1.8 KiB
67 lines
1.8 KiB
2 years ago
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C Copyright(C) 1999-2020 National Technology & Engineering Solutions
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C of Sandia, LLC (NTESS). Under the terms of Contract DE-NA0003525 with
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C NTESS, the U.S. Government retains certain rights in this software.
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C
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C See packages/seacas/LICENSE for details
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SUBROUTINE ETHETA (A7, A8, A2, THETA1, THETA2, THETA, ERR)
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C***********************************************************************
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C SUBROUTINE ETHETA = ITERATIVELY SOLVES THE ELIPTICAL PROBLEM OF
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C FINDING AN "A" DISTANCE GIVEN TWO POINTS ON
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C THE ELIPSE AND A CENTER POINT
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C***********************************************************************
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LOGICAL ERR
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C START WITH 20 INCREMENTS, EACH PASS INCREMENTS DECREASE TEN FOLD
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ANGINC = (THETA2 - THETA1) * .05
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ANG = THETA1
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F1 = ELIPSE (A7, A8, A2, ANG)
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IF (F1 .EQ. 0.0) THEN
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THETA = ANG
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GO TO 110
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END IF
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ANG2 = ANG + ANGINC
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100 CONTINUE
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F2 = ELIPSE (A7, A8, A2, ANG2)
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IF (F2 .EQ. 0.0) THEN
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THETA = ANG2
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ELSE IF (F1*F2 .LT. 0.0) THEN
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THETA = ESOLVE (A7, A8, A2, ANG, ANG2)
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ELSE
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ANG = ANG2
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ANG2 = ANG2 + ANGINC
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IF (ANG2 .LE. THETA2) GO TO 100
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ERR = .TRUE.
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GO TO 120
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END IF
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110 CONTINUE
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120 CONTINUE
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C FIND THE SECOND ROOT IF THE FIRST ONE HAS BEEN LOCATED
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IF(.NOT.ERR)THEN
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ANG=THETA+ANGINC
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F1 = ELIPSE (A7, A8, A2, ANG)
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F2 = ELIPSE (A7, A8, A2, THETA2)
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IF (F1 .EQ. 0.0) THEN
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THETA = ANG
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ELSEIF (F2 .EQ. 0.0) THEN
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THETA = THETA2
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ELSE IF (F1*F2 .LT. 0.0) THEN
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THETA = ESOLVE (A7, A8, A2, ANG, THETA2)
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ELSE
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GO TO 130
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END IF
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END IF
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130 CONTINUE
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RETURN
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END
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