real,allocatable:: tu(:,:),tv(:,:),alpha(:,:)
open(10,file="s2d1.dat")
n=100
allocate(tu(n,n),tv(n,n),alpha(n,n))
tu=0.
tv=0.

tu(1,:)=100.
tv(1,:)=100.

do i=1,n
do j=1,n
alpha(i,j)=0.1
enddo
enddo

nt=100000

do it=1,nt

do i=2,n-1 
do j=2,n-1
tu(i,j)=tv(i,j)+alpha(i,j)*(tv(i+1,j)-4.*tv(i,j)+tv(i-1,j)+tv(i,j+1)+tv(i,j-1))
enddo
enddo

tu(1,:)=100.

if ((it/500)*500.eq.it) then
write(10, '(100f15.5)') tu
endif

tv=tu
enddo

stop
end