function filter(len,curmin)
      integer len
      real curmin
      vector r1,r2,r3,r4
      vector z1,z2,z3,z4
      vector x,c
      do i=1,len
        if (c(i).lt.curmin) then
          r1(i)=-1e-3
          r2(i)=-1e-3
          r3(i)=-1e-3
          r4(i)=-1e-3
        else
          r1(i)=-z1(i)/c(i)
          r2(i)=-z2(i)/c(i)
          r3(i)=-z3(i)/c(i)
          r4(i)=-z4(i)/c(i)
        endif
      enddo
      filter=1
      end