PHI.f90

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!    Copyright (C) 2012 The SPEED FOUNDATION
!    Author: Ilario Mazzieri
!
!    This file is part of SPEED.
!
!    SPEED is free software; you can redistribute it and/or modify it
!    under the terms of the GNU Affero General Public License as
!    published by the Free Software Foundation, either version 3 of the
!    License, or (at your option) any later version.
!
!    SPEED is distributed in the hope that it will be useful, but
!    WITHOUT ANY WARRANTY; without even the implied warranty of
!    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
!    Affero General Public License for more details.
!
!    You should have received a copy of the GNU Affero General Public License
!    along with SPEED.  If not, see <http://www.gnu.org/licenses/>.
 
 
 
      real*8 function phi(ng,csii, csij)
      
      implicit real*8(a-h,o-z)
      integer*4 :: ng
 
      call get_legendre_value_2der(p2der2,p2,p2der,p1,p1der,ng,csii)          
      call get_legendre_value_2der(q2der2,q2,q2der,q1,q1der,ng,csij)   
 
      if(abs(csii - csij).le. 1.e-8) then
          phi = 1.d0  
      else
          phi =  (1.d0-csij**2.d0)*q2der /(ng*(ng+1.d0)*p2*(csii-csij))
          if(abs(phi) .lt. 1.e-10) then
             phi = 0.d0
          endif
      endif
 
      return
      end function phi