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subroutine grad(r,db,i,imin,imax,done,gradd,gradup,graddn)
c grad calculates the derivative of db with respect to r, at
c position r(i).
c input r : radial coordinate (array)
c input db : spin-up and down densities (array)
c input i : counter, i.e. current position = r(i)
c input imin : min value of i
c input imax : max value of i
c in/output done : true if density is splined
c output gradd : grad(density)
c output gradup,graddn : grad(density), spin up and down
implicit logical (a-z)
logical done
double precision r,db,gradd,gradup,graddn,db2,deriv
integer i,imin,imax
dimension r(561),db(2,561),db2(2,561)
common/ggagra/db2
if (.not.done) then
call spline(r,imin+1,imax,db,db2)
done = .true.
endif
gradup = deriv(r,db,db2,1,i,imin,imax)
graddn = deriv(r,db,db2,-1,i,imin,imax)
gradd = gradup + graddn
return
end
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