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44 lines
854 B
Fortran
44 lines
854 B
Fortran
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! ---
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subroutine jBH_elem_fct_grad(alpha, r1, r2, fct, grad1_fct)
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implicit none
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double precision, intent(in) :: alpha, r1(3), r2(3)
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double precision, intent(out) :: fct, grad1_fct(3)
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double precision :: dist, tmp1, tmp2, dist_inv
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dist = (r1(1) - r2(1)) * (r1(1) - r2(1)) &
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+ (r1(2) - r2(2)) * (r1(2) - r2(2)) &
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+ (r1(3) - r2(3)) * (r1(3) - r2(3))
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if(dist .ge. 1d-15) then
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dist_inv = 1.d0/dsqrt( dist )
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dist = dist_inv * dist
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tmp1 = 1.d0 / (1.d0 + alpha * dist)
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fct = alpha * dist * tmp1
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tmp2 = alpha * tmp1 * tmp1 * dist_inv
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grad1_fct(1) = tmp2 * (r1(1) - r2(1))
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grad1_fct(2) = tmp2 * (r1(2) - r2(2))
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grad1_fct(3) = tmp2 * (r1(3) - r2(3))
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else
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grad1_fct(1) = 0.d0
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grad1_fct(2) = 0.d0
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grad1_fct(3) = 0.d0
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fct = 0.d0
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endif
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return
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end
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! ---
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