mirror of
https://github.com/QuantumPackage/qp2.git
synced 2024-11-14 17:33:38 +01:00
58 lines
1.4 KiB
Fortran
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
|
|
|