[子程序] 子程序变量无初值问题

program main
implicit none
call sub2()
end program main

subroutine sub1(X,Y,T,a,b,c,d,ans)
implicit none
real::PI=3.1415926
real::PM=1
real::M=1
real::PL=1
real::PT=1
real,parameter::X0=20
real,parameter::Y0=20
real,parameter::T0=20
real::a(X0,Y0,T0)
real::b(X0,Y0,T0)
real::c(X0,Y0,T0)
real::d(X0,Y0,T0)
real::ans(X0,Y0,T0)
real X
real Y
real T 
real::x1,x2,dx,y1,y2,dy,t1,t2,dt
integer::i,j,k,Nx,Ny,Nt
x1=0.5
x2=10
y1=0.5
y2=10
t1=0.5
t2=10
dx=0.5
dy=0.5
dt=0.5
Nx=(x2-x1)/dx
Ny=(y2-y1)/dy
Nt=(t2-t1)/dt
open(unit=10,file="data1.txt")
do i=1,Nx+1
X=x1+(i-1)*dx
do j=1,Ny+1
y=y1+(j-1)*dy
do k=1,Nt+1 
T=t1+(k-1)*dt
a(i,j,k)=PM*M/(4*(PI**1)*(PL**0.5)*(PT**0.5)*(T**1))
b(i,j,k)=-1/(2*PL*T)
c(i,j,k)=((X-T)/(2*PL*T))**2
d(i,j,k)=((X-T)**2)/(4*PL*T)+(y**2/(4*PT*T))
ans(i,j,k)=(PM*M/(4*(PI**1)*(PL**0.5)*(PT**0.5)*(T**2)))*((-1/(2*PL*T))+((((X-T)/(2*PL*T))**2)**2))*(exp(-(((X-T)**2)/(4*PL*T)+(y**2/(4*PT*T)))))
write(10,"('(',f5.2,',',f5.2,','f5.2')=',(2X,F9.6),(2X,F9.6),(2X,F9.6),(2X,F9.6),(2X,F9.6))") X,Y,T,a(i,j,k),b(i,j,k),c(i,j,k),d(i,j,k),ans(i,j,k)
end do
end do
end do
return
end

subroutine sub2()
implicit none
integer,parameter:: i0=20
integer,parameter:: j0=20
integer,parameter:: k0=20
integer i
integer j
integer k
real X
real Y
real T
real::a(i0,j0,k0)
real::b(i0,j0,k0)
real::c(i0,j0,k0)
real::d(i0,j0,k0)
real::ans(i0,j0,k0)
call sub1(X,Y,T,a,b,c,d,ans)
open(unit=11,file='data2.txt')
do i=1,i0
do j=1,j0
do k=1,k0
if (ans(i,j,k)>-0.01.and.ans(i,j,k)<0.01) then
write(11,"('(',f5.2,',',f5.2,','f5.2')=',(2X,F9.6),(2X,F9.6),(2X,F9.6),(2X,F9.6),(2X,F9.6))") X,Y,T,a(i,j,k),b(i,j,k),c(i,j,k),d(i,j,k),ans(i,j,k)
end if
end do
end do
end do
return 
end