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qp2/src/ao_two_e_ints/gauss_legendre.irp.f
Anthony Scemama 77186e0560
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Cleaned cosgtos
2023-06-01 11:11:29 +02:00

58 lines
1.4 KiB
Fortran

BEGIN_PROVIDER [ double precision, gauleg_t2, (n_pt_max_integrals,n_pt_max_integrals/2) ]
&BEGIN_PROVIDER [ double precision, gauleg_w, (n_pt_max_integrals,n_pt_max_integrals/2) ]
implicit none
BEGIN_DOC
! t_w(i,1,k) = w(i)
! t_w(i,2,k) = t(i)
END_DOC
integer :: i,j,l
l=0
do i = 2,n_pt_max_integrals,2
l = l+1
call gauleg(0.d0,1.d0,gauleg_t2(1,l),gauleg_w(1,l),i)
do j=1,i
gauleg_t2(j,l) *= gauleg_t2(j,l)
enddo
enddo
END_PROVIDER
subroutine gauleg(x1,x2,x,w,n)
implicit none
BEGIN_DOC
! Gauss-Legendre
END_DOC
integer, intent(in) :: n
double precision, intent(in) :: x1, x2
double precision, intent (out) :: x(n),w(n)
double precision, parameter :: eps=3.d-14
integer :: m,i,j
double precision :: xm, xl, z, z1, p1, p2, p3, pp, dn
m=(n+1)/2
xm=0.5d0*(x2+x1)
xl=0.5d0*(x2-x1)
dn = dble(n)
do i=1,m
z=dcos(3.141592654d0*(dble(i)-.25d0)/(dble(n)+.5d0))
z1 = z+1.d0
do while (dabs(z-z1) > eps)
p1=1.d0
p2=0.d0
do j=1,n
p3=p2
p2=p1
p1=(dble(j+j-1)*z*p2-dble(j-1)*p3)/j
enddo
pp=dn*(z*p1-p2)/(z*z-1.d0)
z1=z
z=z1-p1/pp
end do
x(i)=xm-xl*z
x(n+1-i)=xm+xl*z
w(i)=(xl+xl)/((1.d0-z*z)*pp*pp)
w(n+1-i)=w(i)
enddo
end