[求助] 这个product的使用报错，不知道如何更改

Subroutine Wii_()
Implicit none
real*8::x(11),y(11),pi=3.141592653589793,L
Integer::N,i,j
L=1
N=11
Do i=1,N,1
    x(i)=(L/2)*(1-cos(((i-1)/(N-1))*pi))
Do j=1,N,1
y(j)=(L/2)*(1-cos(((j-1)/(N-1))*pi))
  END Do
  END Do
end Subroutine Wii_
    
    program main_mik
    Implicit real*8(a-z)
    real*8::G(1),W(1),x(11),y(11)
    Integer::k
    k=1
call  Wii_()
 G(k)=product(x(i)-y(j),y(j)/=x(i))
 W(k)=1/G(k)
  write(*,*)"W(k)=W(k)"
  end program main_mik

Subroutine Wii_(x,y)
  Implicit none
  real*8::x(11),y(11),pi=acos(-1.0),L
  Integer::N,i,j
  L=1
  N=11
  Do i=1,N
    x(i)=(L/2)*(1-cos(((i-1.0)/(N-1.0))*pi))
  END Do
  Do j=1,N
    y(j)=(L/2)*(1-sin(((j-1.0)/(N-1.0))*pi))
  END Do
end Subroutine Wii_

program main_mik
  Implicit real*8(a-z)
  real*8::G(1),W(1),x(11),y(11)
  Integer::k
  k=1
  call  Wii_(x,y)
  G(k)=product(x-y,x/=y)
  W(k)=1/G(k)
  write(*,*)"W(k)=",W(k)
end program main_mik