program gongcheng
implicit none
real(kind=8),parameter::G=1.3218278962236387e-42
real(kind=8),parameter::m0=1.1158032783756145e60
real(kind=8),parameter::R=20.0e18
real(kind=8),parameter::pi=3.1415926535
real(kind=8),parameter::h0=1.0e15
real(kind=8)::p0(100)
common p0
real,external::f
real,external::q
integer::i
real(kind=8)::rho(991),ene(991),pre(991)
real(kind=8)::x(20000),z(20000),y(20000),p(20000),m(20000),e(20000)
double precision h,n,k1,k2,k3,k4,M1,M2,M3,M4
do i=1,100
p0(i)=i
call rungekutta(x,y,z,f,q)
write(*,*)x(i+1),z(i+1)/m0
end do
end program
function f(r,p,m)
implicit none
real(kind=8)::r(20000.d0),p(20000.d0),m(20000.d0),e(20000.d0)
real(kind=8)::f(20000)
real(kind=8)::rho(990.d0),ene(990.d0),pre(990.d0)
integer::i
real(kind=8),parameter::G=1.3218278962236387e-42
real(kind=8),parameter::pi=3.1415926535
open(unit=26,file="EOS.txt")
do i=1.d0,990.d0
read(26,*)rho(i),ene(i),pre(i)
end do
call spline(pre,ene,990,p,20000,e)
f=-(e+p)*(G*m+4*pi*G*(r**3)*p)/(r*(r-2*G*m))
return
end
function q(r,p,m)
implicit none
real(kind=8)::e(20000.d0),p(20000.d0),r(20000.d0),m(20000.d0)
integer::i
real(kind=8)::rho(990.d0),ene(990.d0),pre(990.d0)
real::q(20000)
real(kind=8),parameter::pi=3.1415926535
open(unit=26,file="EOS.txt")
do i=1.d0,990.d0
read(26,*)rho(i),ene(i),pre(i)
end do
call spline(pre,ene,990,p,20000,e)
q=4*pi*e*r**2
return
end
subroutine rungekutta(x,y,z,f,q)
real(kind=8)::x(20000),z(20000),y(20000),p(20000),m(20000)
integer::i
real,external::f
real,external::q
double precision h,n,k1,k2,k3,k4,M1,M2,M3,M4
n=20.0e18/1.0e15
h=1.0e15
x(1)=0.0
y(1)=p0
z(1)=0.0
do i=1,n-1
y(i)=p(i)
z(i)=m(i)
x(i+1)=(i+1)*h
k1=f(x(i),y(i))
M1=q(x(i),y(i))
k2=f(x(i)+0.5*h,y(i)+0.5*h*k1)
M2=q(x(i)+0.5*h,y(i)+0.5*h*M1)
k3=f(x(i)+0.5*h,y(i)+0.5*h*k2)
M3=q(x(i)+0.5*h,y(i)+0.5*h*M2)
k4=f(x(i)+h,y(i)+h*k3)
M4=q(x(i)+h,y(i)+h*M3)
y(i+1)=y(i)+h*(k1+k2+k3+k4)/6
z(i+1)=z(i)+h*(M1+M2+M3+M4)/6
if (y(i+1)<=1.0*10**(-5))then
exit
end if
end do
end subroutine rungekutta
subroutine spline(x,y,n,sx,m,f) !x,y:差值基点坐标,n:节点个数,sx:需要返回差值数值的x坐标,m:sx的容量,f:差值结果返回值
implicit none
integer:: i, j, k, m, n, n1, n2
Real(kind=8)::x(n),y(n),sx(m),f(m)
Real(kind=8):: s2(n), h(n), dy(n), s(n), e(n) !直接都给数组定义N的空间大小,方便调用
Real(kind=8):: z, h1, h2, h3, h4
n1=n-1!间距个数
n2=n-2!内点个数
do i = 1,n1
h(i) = x(i+1) - x(i)!计算点间距
dy(i) = (y(i+1) - y(i) ) / H(i)!计算斜率sj
end do
S2(1) = 0.d0; S2(N) = 0.d0!自然边界条件,两侧二阶导数为零
DO i = 2, N1!求解内结点处的二阶导数
S2(i) = 6.d0 * ( DY(i) - DY(i-1) )
ENDDO
Z = 0.5d0 / ( H(1) + H(2) )
S(1) = -H(2) * Z
E(1) = S2(2) * Z
DO i = 2, N2
k = i - 1
j = i + 1
Z = 1.d0 / ( 2.d0*( H(i)+H(j) ) + H(i)*S(k) )
S(i) = -H(j) * Z
E(i) = ( S2(j)-H(i)*E(k) ) * Z
ENDDO
S2(N1) = E(N2)
DO i = N2, 2, -1
k = i - 1
S2(i) = S(k)*S2(i+1) + E(k)
ENDDO
DO i = 1, N1
S(i) = ( S2(i+1) - S2(i) ) / H(i)
ENDDO
!具体求结果
i = 2
k = 1
DO j = 1, M
DO
IF(sx(j)>x(i)) THEN
k = i
i = i + 1
ELSE
EXIT
ENDIF
ENDDO
H1 = SX(i) - X(k)
H2 = SX (i)- X(i)
H3 = H1 * H2
H4 = S2(k) + H1*S(k)
Z = ( S2(i) + S2(k) + H4 ) / 6.d0
F(j) = Y(k) + H1*DY(k) + H3*Z
ENDDO
end subroutine spline
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调用的数据
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