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42 lines
952 B
Fortran
42 lines
952 B
Fortran
subroutine uniform_montecarlo(a,nmax,energy)
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implicit none
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double precision, intent(in) :: a
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integer*8 , intent(in) :: nmax
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double precision, intent(out) :: energy
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integer*8 :: istep
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double precision :: norm, r(3), w
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double precision, external :: e_loc, psi
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energy = 0.d0
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norm = 0.d0
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do istep = 1,nmax
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call random_number(r)
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r(:) = -5.d0 + 10.d0*r(:)
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w = psi(a,r)
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w = w*w
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norm = norm + w
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energy = energy + w * e_loc(a,r)
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end do
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energy = energy / norm
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end subroutine uniform_montecarlo
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program qmc
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implicit none
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double precision, parameter :: a = 0.9
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integer*8 , parameter :: nmax = 100000
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integer , parameter :: nruns = 30
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integer :: irun
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double precision :: X(nruns)
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double precision :: ave, err
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do irun=1,nruns
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call uniform_montecarlo(a,nmax,X(irun))
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enddo
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call ave_error(X,nruns,ave,err)
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print *, 'E = ', ave, '+/-', err
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end program qmc
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