anchor.diff:   ! I n i t !
    !=!=!=!=!=!
   
  - f=fourpi**2
  + f=fourpi*fourpi
   
    theta_AC0=dacos( (a(3)-c(3))/ac )
    phi_AC0=datan2((a(2)-c(2))/ac,(a(1)-c(1))/ac)
  
positive.code:         DIMENSION PM(0:100,0:100)
          MM=100
          pi=dacos(-1.d0)
          iabs_m=iabs(m)
          if(iabs_m.gt.l)stop 'm must be between -l and l'
          factor= dsqrt( ((2*l+1)*fact(l-iabs_m))/(4.d0*pi*fact(l+iabs_m)) )
          if(dabs(x).gt.1.d0)then
           print*,'pb. in ylm_no'
           print*,'x=',x
  
negative.code:   ! Int f_0
    coef_nk=1.d0/dble_fact( n+n+1 )
    expo=0.5d0*dfloat(n+l+1)
    crochet=dble_fact(n+l-1)/(gam+gam)**expo
    if(mod(n+l,2).eq.0)crochet=crochet*dsqrt(0.5d0*pi)
  
    f_0 = coef_nk*a**n*crochet
  