1 files changed, 92 insertions, 0 deletions
diff --git a/Utilib/src/ALGUER.f b/Utilib/src/ALGUER.f
new file mode 100644
index 0000000..ddd93a1
--- /dev/null
+++ b/Utilib/src/ALGUER.f
@@ -0,0 +1,92 @@
+*DECK ALGUER
+      SUBROUTINE ALGUER(A,M,X,ITS,LFAIL)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* find one root of a polynomial.
+*
+*Copyright:
+* Copyright (C) 1993 Ecole Polytechnique de Montreal
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU Lesser General Public
+* License as published by the Free Software Foundation; either
+* version 2.1 of the License, or (at your option) any later version
+*
+*Author(s): A. Hebert
+*
+*Parameters: input
+* A       polynomial coefficients. DIMENSION A(M+1)
+* M       polynomial order.
+*
+*Parameters: output
+* X       complex single root.
+* ITS     number of iterations.
+* LFAIL   set to .true. in case of failure.
+*
+*-----------------------------------------------------------------------
+*
+      IMPLICIT DOUBLE PRECISION(A-H,O-Z)
+*----
+*  SUBROUTINE ARGUMENTS
+*----
+      INTEGER M,ITS
+      COMPLEX*16 A(M+1),X
+      LOGICAL LFAIL
+*----
+*  LOCAL VARIABLES
+*----
+      INTEGER MAXIT,MR,MT
+      DOUBLE PRECISION EPSS
+      PARAMETER (EPSS=2.D-7,MR=8,MT=10,MAXIT=MT*MR)
+      INTEGER ITER,J
+      DOUBLE PRECISION ABX,ABP,ABM,ERR,FRAC(MR)
+      COMPLEX*16 DX,X1,B,D,F,G,H,SQ,GP,GM,G2,TMP
+      SAVE FRAC
+      DATA FRAC /.5D0,.25D0,.75D0,.13D0,.38D0,.62D0,.88D0,1.D0/
+*
+      LFAIL=.FALSE.
+      DO 12 ITER=1,MAXIT
+        ITS=ITER
+        B=A(M+1)
+        ERR=ABS(B)
+        D=CMPLX(0.D0,0.D0,KIND=KIND(D))
+        F=CMPLX(0.D0,0.D0,KIND=KIND(F))
+        ABX=ABS(X)
+        DO 11 J=M,1,-1
+          F=X*F+D
+          D=X*D+B
+          B=X*B+A(J)
+          ERR=ABS(B)+ABX*ERR
+11      CONTINUE
+        ERR=EPSS*ERR
+        IF(ABS(B).LE.ERR) THEN
+          RETURN
+        ELSE
+          G=D/B
+          G2=G*G
+          H=G2-2.D0*F/B
+          SQ=SQRT((M-1)*(M*H-G2))
+          GP=G+SQ
+          GM=G-SQ
+          ABP=ABS(GP)
+          ABM=ABS(GM)
+          IF(ABP.LT.ABM) GP=GM
+          IF (MAX(ABP,ABM).GT.0.D0) THEN
+            DX=M/GP
+          ELSE
+            TMP=CMPLX(LOG(1.D0+ABX),DBLE(ITER),KIND=KIND(TMP))
+            DX=EXP(TMP)
+          ENDIF
+        ENDIF
+        X1=X-DX
+        IF(X.EQ.X1)RETURN
+        IF (MOD(ITER,MT).NE.0) THEN
+          X=X1
+        ELSE
+          X=X-DX*FRAC(ITER/MT)
+        ENDIF
+12    CONTINUE
+      LFAIL=.TRUE.
+      RETURN
+      END