module guass
    contains
subroutine solve_guass(A,b,x,N)
implicit none
integer::N,i,j,k
real::A(N,N),b(N),x(N)
real::temp

do k=1,N-1,1
    do i=k+1,N,1
        temp=A(i,k)/A(k,k)
        do j=k,N,1
            A(i,j)=A(i,j)-temp*A(k,i)
            b(i)=b(i)-temp*b(k)
        end do
    end do
end do

call solve_uptri(A,b,x,N)
end subroutine

subroutine solve_uptri(A,b,x,N)
implicit none
integer::N
real::A(N,N),x(N),b(N)
integer::j,k
real::temp

x(N)=b(N)/A(N,N)

do k=N-1,1,-1
    temp=0
    do j=k+1,N,1
        temp=temp+A(k,j)*x(j)
    end do
    x(k)=(b(k)-temp)/A(k,k)
end do
end subroutine

end module