program pos
implicit none
double precision vreal(2),vfcc(2),v(2),u,x(3),dx(3),c,xreal(3),a,vlength
integer i,j
external vlength

read(5,*)c

a=8.490540*0.529177 !a.u. to ang. this is FeSi
a=4.7097 !RuSi

!real structure
vreal(1)=0.12800 !Ru
vreal(2)=0.83600 !Si


!fcc
vfcc(1)=0.25d0
vfcc(2)=0.75d0


v(1)=c*vfcc(1) + (1.d0-c)* vreal(1)
v(2)=c*vfcc(2) + (1.d0-c)* vreal(2)


write(*,*)c
write(*,*)v
write(*,*)

dx=0.d0
if (c.eq.1.d0) then
dx(1)=0.25
dx(2)=-0.25
dx(3)=-0.25
endif

!half way
!v(1)=0.1929
!v(2)=0.797
!dx=0.d0




do i=1,2
   u=v(i)

   x(1)=u
   x(2)=u
   x(3)=u

   xreal(1)=vreal(i)
   xreal(2)=vreal(i)
   xreal(3)=vreal(i)

   x=x-dx
   xreal=xreal-dx

   
   write(*,'(10F12.8)') x , vlength(x,xreal)*a
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

   x(1)=0.5d0-u
   x(2)=1.d0-u
   x(3)=0.5d0+u
   xreal(1)=0.5d0-vreal(i)
   xreal(2)=1.d0-vreal(i)
   xreal(3)=0.5d0+vreal(i)

   x=x-dx
   xreal=xreal-dx
   do j=1,3
      if (x(j).gt.1.d0) x(j)=x(j)-1.d0
      if (x(j).lt.0.d0) x(j)=x(j)+1.d0
      if (xreal(j).gt.1.d0) xreal(j)=xreal(j)-1.d0
      if (xreal(j).lt.0.d0) xreal(j)=xreal(j)+1.d0
   enddo
   
   write(*,'(10F12.8)') x, vlength(x,xreal)*a
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


   x(1)=0.5d0+u
   x(2)=0.5d0-u
   x(3)=1.d0-u
   xreal(1)=0.5d0+vreal(i)
   xreal(2)=0.5d0-vreal(i)
   xreal(3)=1.d0-vreal(i)


   x=x-dx
   xreal=xreal-dx
   do j=1,3
      if (x(j).gt.1.d0) x(j)=x(j)-1.d0
      if (x(j).lt.0.d0) x(j)=x(j)+1.d0
      if (xreal(j).gt.1.d0) xreal(j)=xreal(j)-1.d0
      if (xreal(j).lt.0.d0) xreal(j)=xreal(j)+1.d0
   enddo



   write(*,'(10F12.8)') x, vlength(x,xreal)*a
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

   x(1)=1.d0-u
   x(2)=0.5d0+u
   x(3)=0.5d0-u
   xreal(1)=1.d0-vreal(i)
   xreal(2)=.5d0+vreal(i)
   xreal(3)=0.5d0-vreal(i)


   x=x-dx
   xreal=xreal-dx
   do j=1,3
      if (x(j).gt.1.d0) x(j)=x(j)-1.d0
      if (x(j).lt.0.d0) x(j)=x(j)+1.d0
      if (xreal(j).gt.1.d0) xreal(j)=xreal(j)-1.d0
      if (xreal(j).lt.0.d0) xreal(j)=xreal(j)+1.d0
   enddo


   write(*,'(10F12.8)') x, vlength(x,xreal)*a
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

write(*,*)
enddo
end


double precision function vlength(x,y)
implicit none
double precision x(3),y(3),d
integer i

d=0.d0
do i=1,3
   d=d+(x(i)-y(i))**2.d0
enddo
vlength=dsqrt(d)

end