# Category : Miscellaneous Language Source Code

Archive : FORTRN77.ZIP

Filename : NABAIR.FOR

C

C BAIRSTOW'S METHOD FOR FINDING ROOTS OF NTH DEGREE POLYNOMIAL

C WITH REAL COEFFICIENTS. POLYNOMIAL IS OF THE FORM

C A(1)X**N + A(2)X**(N - 1) + A(3)X**(N-2) + ... + A(N)X + A(N+1).

C

DIMENSION A(1), B(1), C(1), ROOT(1)

IITAG = ITAG

ITAG = 0

D = A(1)

DO 10 I = 1,N

10 A(I) = A(I + 1)/D

40 IF(N.GT.1) GO TO 43

ITAG = ITAG + 1

L = ITAG + ITAG

ROOT(L) = 0.

ROOT(L-1) = -A(1)

N = ITAG

ITAG = 4

RETURN

43 IF(N.GT.2) GO TO 46

P = A(1)

Q = A(2)

GO TO 8

46 P = P1

Q = Q1

M = 1

51 B(1) = A(1) - P

B(2) = A(2) - P*B(1) - Q

L = N - 1

C(1) = B(1) - P

C(2) = B(2) - P*C(1) - Q

IF(L.EQ.2) L = 3

DO 7 J = 3,L

B(J) = A(J) - P*B(J-1) - Q*B(J-2)

7 C(J) = B(J) - P*C(J-1) - Q*C(J-2)

L = N - 1

CBARL = C(L) - B(L)

DEN = -CBARL

IF(N.NE.3) DEN = DEN*C(N-3)

DEN = DEN + C(N-2)*C(N-2)

IF(DEN.NE.0.0) GO TO 1

N = ITAG

ITAG = 1

RETURN

1 B(N) = A(N) - P*B(N-1) - Q*B(N-2)

DELTP = -B(N)

IF(N.NE.3) DELTP = DELTP*C(N-3)

DELTP = (B(N-1)*C(N-2) + DELTP)/DEN

DELTQ = (B(N)*C(N-2) - B(N-1)*CBARL)/DEN

P = P + DELTP

Q = Q + DELTQ

SUM = ABS(DELTP) + ABS(DELTQ)

IF(M.EQ.1) SUM1 = SUM

IF(M.NE.5.OR.SUM.LE.SUM1) GO TO 11

N = ITAG

ITAG = 2

RETURN

11 IF(SUM.LE.EPS) GO TO 8

IF(M.LT.IITAG) GO TO 2

N = ITAG

ITAG = 3

RETURN

2 M = M + 1

GO TO 51

8 D = -P*0.5

ITAG = ITAG + 2

F = Q - D*D

E = SQRT(ABS(F))

L = ITAG + ITAG

IF(F.GT.0.0) GO TO 31

ROOT(L) = 0.0

ROOT(L - 1) = D-E

ROOT(L-2) = 0.0

ROOT(L-3) = D + E

GO TO 32

31 ROOT(L) = -E

ROOT(L - 1) = D

ROOT(L - 2) = E

ROOT(L - 3) = D

32 N = N - 2

IF(N.GT.0) GO TO 81

N = ITAG

ITAG = 4

RETURN

81 DO 82 I = 1,N

82 A(I) = B(I)

GO TO 40

RETURN

END

Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

This is so awesome! 😀 I’d be cool if you could download an entire archive of this at once, though.

But one thing that puzzles me is the “mtswslnkmcjklsdlsbdmMICROSOFT” string. There is an article about it here. It is definitely worth a read: http://www.os2museum.com/wp/mtswslnk/