subroutine lubksb_dp(a,n,np,indx,b)                              

c     jul 2011 malv+fgg

      implicit none

      integer n,np
      real*8 a(np,np),b(n) 
      integer indx(n)

      real*8 sum
      integer ii, ll, i, j

      ii=0                                                              
      do 12 i=1,n                                                             
        ll=indx(i)                                                            
        sum=b(ll)                                                             
        b(ll)=b(i)                                                            
        if (ii.ne.0)then                                                      
          do 11 j=ii,i-1                                                      
            sum=sum-a(i,j)*b(j)                                               
11        continue                                                            
        else if (sum.ne.0.0) then                       
          ii=i                                                                
        endif                                                                 
        b(i)=sum                                                              
12    continue                                                                
      do 14 i=n,1,-1                                                          
        sum=b(i)                                                              
        if(i.lt.n)then                                                        
          do 13 j=i+1,n                                                       
            sum=sum-a(i,j)*b(j)                                               
13        continue                                                            
        endif                                                                 
        b(i)=sum/a(i,i)                                                       
14    continue                                                                
      return                                                                  
      end