      SUBROUTINE  DSCAL(N,DA,DX,INCX)                                           
C                                                                               
C     SCALES A VECTOR BY A CONSTANT.                                            
C     USES UNROLLED LOOPS FOR INCREMENT EQUAL TO ONE.                           
C     JACK DONGARRA, LINPACK, 3/11/78.                                          
C                                                                               
      DOUBLE PRECISION DA,DX(1)                                                 
      INTEGER I,INCX,M,MP1,N,NINCX                                              
C                                                                               
      IF(N.LE.0)RETURN                                                          
      IF(INCX.EQ.1)GO TO 20                                                     
C                                                                               
C        CODE FOR INCREMENT NOT EQUAL TO 1                                      
C                                                                               
      NINCX = N*INCX                                                            
      DO 10 I = 1,NINCX,INCX                                                    
        DX(I) = DA*DX(I)                                                        
   10 CONTINUE                                                                  
      RETURN                                                                    
C                                                                               
C        CODE FOR INCREMENT EQUAL TO 1                                          
C                                                                               
C                                                                               
C        CLEAN-UP LOOP                                                          
C                                                                               
   20 M = MOD(N,5)                                                              
      IF( M .EQ. 0 ) GO TO 40                                                   
      DO 30 I = 1,M                                                             
        DX(I) = DA*DX(I)                                                        
   30 CONTINUE                                                                  
      IF( N .LT. 5 ) RETURN                                                     
   40 MP1 = M + 1                                                               
      DO 50 I = MP1,N,5                                                         
        DX(I) = DA*DX(I)                                                        
        DX(I + 1) = DA*DX(I + 1)                                                
        DX(I + 2) = DA*DX(I + 2)                                                
        DX(I + 3) = DA*DX(I + 3)                                                
        DX(I + 4) = DA*DX(I + 4)                                                
   50 CONTINUE                                                                  
      RETURN                                                                    
      END                                                                       
