57 lines
937 B
Fortran
57 lines
937 B
Fortran
program square
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implicit none
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integer :: nside,nsite,nelec
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integer :: ix,iy,iz,i
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real*16 :: factor,bbfac
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real*16 :: uee,ubb,eta0,aux
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real*16 :: start,finish
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real*16,allocatable :: sin2(:)
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open(unit=10,file='input')
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read(10,*) nside
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close(10)
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call cpu_time(start)
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nsite = nside
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nelec = nside**2
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bbfac = 1.139479116668307748953273191122493968q0
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write(6,*) "total number of electrons",nelec
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allocate(sin2(nsite))
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factor=acos(-1q0)/nsite
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do i = 0, nsite-1
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sin2(i+1) = (sin(factor*i))**2
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enddo
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uee = 0q0
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do ix = 0, nsite-1
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do iy = 0, nsite-1
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if (ix+iy==0) cycle
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aux = sqrt(sin2(ix+1)+sin2(iy+1))
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uee = uee + 1q0/aux
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enddo
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enddo
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factor=sqrt(acos(-1q0))/(nsite*2q0)
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uee=uee*factor
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ubb = nelec*bbfac/nside
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eta0 = uee - ubb
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print*,'eta0 (in Ry and Ha) =', 2q0*eta0, eta0
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print*, uee,ubb
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deallocate(sin2)
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call cpu_time(finish)
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print '("Time = ",f12.3," seconds.")',finish-start
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end program square
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