SUBROUTINE ZSU(A,INT,X,N,NC,EMACH)  
      IMPLICIT NONE 
C     ------------------------------------------------------------------  
C     ZSU  IS  A STANDARD BACK-SUBSTITUTION  SUBROUTINE  USING THE   
C     OUTPUT OF ZGE TO CALCULATE  A-INVERSE TIMES X, RETURNED IN X  
C     ------------------------------------------------------------------  
C  
C ..  SCALAR ARGUMENTS  ..  
C  
      INTEGER N,NC  
      REAL*8 EMACH  
C  
C ..  ARRAY ARGUMENTS  ..  
C  
      INTEGER    INT(NC)  
      COMPLEX*16 A(NC,NC),X(NC)  
C  
C ..  LOCAL SCALARS  ..  
C  
      INTEGER    I,II,IN,J,IJ  
      COMPLEX*16 DUM  
C  
C ..  INTRINSIC FUNCTIONS  ..  
C  
*      INTRINSIC ABS  
C     ------------------------------------------------------------------  
C  
      DO 5 II=2,N  
      I=II-1  
      IF(INT(I)-I)1,2,1    !If INT(I).NE.I switch the I-th and INT(I)-th 
                           !elements of the vector X
   1  IN=INT(I)  
      DUM=X(IN)  
      X(IN)=X(I)  
      X(I)=DUM  
*
* Forming a matrix product
*
   2  DO 4 J=II,N  
      IF(ABS(A(J,I))-EMACH)4,4,3  
   3  X(J)=X(J)-A(J,I)*X(I)  
   4  CONTINUE  

   5  CONTINUE               !the I-th column of A multiplied by X(I) 
                             !subtracted from X 
*
      DO 10 II=1,N  
      I=N-II+1  
      IJ=I+1  
      IF(I-N)6,8,6  
   6  DO 7 J=IJ,N  
   7  X(I)=X(I)-A(I,J)*X(J)  
   8  IF(ABS(A(I,I))-EMACH*1.0D-7)9,10,10  
   9  A(I,I)=EMACH*1.0D-7*(1.D0,1.D0)  
  10  X(I)=X(I)/A(I,I)  
      RETURN  
      END