Question

我使用Euler-Richardson算法为三体问题编写了一个简单的Fortran程序。由于某种原因，输出文件只提供NaN。问题是通过使用子程序或函数来解决的吗？

PROGRAM Threebody
IMPLICIT none



!************** Variable declarations ***************

!real(8), parameter :: G = 6.6738D-11

INTEGER :: IOSTAT, dt, t_step, io_error, i
DOUBLE PRECISION:: st, g, m0, m1, m2, force0x, force0y, force1x, force1y, force2x, force2y, n0, n1, n2, x0,v0,x1,v1,x2,v2,y0,w0,y1
DOUBLE PRECISION:: w1,y2,w2

m0 = 1.d0                               ! the masses of the three bodies
m1 = 1.d0
m2 = 1.d0

g = 9.80d0                              ! m/s^2 s due to gravity

t_step = 1

y0 = 0.d0                           
x0 = 0.d0
v0 = 0.d0                               
w0 = 0.d0

y1 = 0.d0                           
x1 = 1.d0
v1 = 2.d0                               
w1 = 1.118d0

y2 = 0.d0                           
x2 = -1.d0
v2 = -1.118d0                               
w2 = 0.d0


dt = 1  ! time step

OPEN(unit=5, file='out.txt', status='replace',action='write', IOSTAT=io_error)
OPEN(unit=6, file='out1.txt', status='replace',action='write', IOSTAT=io_error)
OPEN(unit=7, file='out2.txt', status='replace',action='write', IOSTAT=io_error)





! particle no.1
DO i=0,1000,t_step                          ! 1000 is the total time

st=i!/10.d0

n0 = sqrt(((x2 - x1)**2 + (y2 - y1)**2)**3)

force0x  = (- m1*(( x0 - x1 ) / n2)) - (m2*(( x0 - x2 ) / n1))

x0 = x0 + (w0 + 0.5*force0x*st)*st
w0 = w0 + force0x*st

force0y  = (- m1 * (( y0 - y1 ) / n2)) - (m2 * (( y0 - y2 ) / n1))

y0 = y0 + (v0 + 0.5*force0y*st)*st
v0 = v0 + force0y*st


WRITE(5,*) i*t_step, x0, y0, n0

END DO




! particle no.2
DO i=0,1000,dt              

st=i

n1 = sqrt(((x0 - x2 )**2 + (y0 - y2)**2)**3) 

force1x  = (- m2 * (( x1 - x0 ) / (n0))) - m0 * (( x1 - x2 ) / n2)

x1 = x1 + (w1 + 0.5*force1x*st)*st
w1 = w1 + force1x*st

force1y  = (- m2 * ( y1 - y0 ) / n0) - (m0 * (( y1 - y2 ) / n2))

y1 = y1 + (v1 + 0.5*force1y*st)*st
v1 = v1 + force1y*st


WRITE(6,*) i*t_step, x1, y1
END DO




! particle no.3
DO i=0,1000,dt  

st=i            

n2 = sqrt ( ( ( x1 - x0 )**2 + ( y1 - y0 )**2 )**3 )

force2x = (- m0 * (( x2 - x0 ) / n1)) - (m1 * (( x2 - x1 ) / n0))

x2 = x2 + (w2 + 0.5*force2x*st)*st
w2 = w2 + force2x*st

force2y = (- m0 * (( y2 - y0 ) / n1)) - (m1 * (( y2 - y1 ) / n0))

y2 = y2 + (v2 + 0.5*force2y*st)*st
v2 = v2 + force2y*st


WRITE(7,*) i*t_step, x2, y2, n2
END DO


CLOSE(unit=5)
CLOSE(unit=6)
CLOSE(unit=7)

END PROGRAM Threebody

Answer 1

在gfortran中使用-Wall进行编译会给你一个提示：

f.f90:56:0: warning: ‘n1’ may be used uninitialized in this function [-Wmaybe-uninitialized]
      force0x  = (- m1*(( x0 - x1 ) / n2)) - (m2*(( x0 - x2 ) / n1))

n1和n2未初始化，因此它们可能包含任何内容。在我的情况下，6.95e-310，导致force0x给出NaN。

要调试此功能，您可以在屏幕上打印变量以检查它们何时变为NaN。为此，请不要使用10以下的单位，因为它们可能会被保留。我认为第5单元是标准输出，因此通过重复使用，您无法在屏幕上打印任何内容。

Fortran初学者 - 输出文件显示NaN

1 个答案: