- xj=c(1,j)+0.5*dxj-xmedi
- yj=c(2,j)+0.5*dyj-ymedi
- zj=c(3,j)+0.5*dzj-zmedi
+ xj=c(1,j)+0.5*dxj
+ yj=c(2,j)+0.5*dyj
+ zj=c(3,j)+0.5*dzj
+ xj=mod(xj,boxxsize)
+ if (xj.lt.0) xj=xj+boxxsize
+ yj=mod(yj,boxysize)
+ if (yj.lt.0) yj=yj+boxysize
+ zj=mod(zj,boxzsize)
+ if (zj.lt.0) zj=zj+boxzsize
+ dist_init=(xj-xi)**2+(yj-yi)**2+(zj-zi)**2
+ xj_safe=xj
+ yj_safe=yj
+ zj_safe=zj
+ isubchap=0
+ do xshift=-1,1
+ do yshift=-1,1
+ do zshift=-1,1
+ xj=xj_safe+xshift*boxxsize
+ yj=yj_safe+yshift*boxysize
+ zj=zj_safe+zshift*boxzsize
+ dist_temp=(xj-xi)**2+(yj-yi)**2+(zj-zi)**2
+ if(dist_temp.lt.dist_init) then
+ dist_init=dist_temp
+ xj_temp=xj
+ yj_temp=yj
+ zj_temp=zj
+ isubchap=1
+ endif
+ enddo
+ enddo
+ enddo
+ if (isubchap.eq.1) then
+ xj=xj_temp-xmedi
+ yj=yj_temp-ymedi
+ zj=zj_temp-zmedi
+ else
+ xj=xj_safe-xmedi
+ yj=yj_safe-ymedi
+ zj=zj_safe-zmedi
+ endif
+ rij=xj*xj+yj*yj+zj*zj
+ sss=sscale(sqrt(rij))
+ sssgrad=sscagrad(sqrt(rij))