1!
2!     CalculiX - A 3-dimensional finite element program
3!              Copyright (C) 1998-2021 Guido Dhondt
4!
5!     This program is free software; you can redistribute it and/or
6!     modify it under the terms of the GNU General Public License as
7!     published by the Free Software Foundation(version 2);
8!
9!
10!     This program is distributed in the hope that it will be useful,
11!     but WITHOUT ANY WARRANTY; without even the implied warranty of
12!     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13!     GNU General Public License for more details.
14!
15!     You should have received a copy of the GNU General Public License
16!     along with this program; if not, write to the Free Software
17!     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
18!
19!     d{K(X)}/dX
20!
21!     author: Yannick Muller
22!
23      subroutine dKdX(x,u,uprime,rpar,ipar)
24!
25      implicit none
26      integer ipar
27      real*8 x,u(1),uprime(1),rpar(*),zk0,phi
28!
29!     defining the parameters
30      phi=rpar(1)
31      zk0=rpar(3)
32
33      uprime(1)=datan(1.d0)*0.315d0/(phi)*x**1.6d0*
34     &    ((zk0*u(1))**1.75d0-
35     &    (dabs(1.d0-u(1)))**1.75d0*(1.d0-u(1))/dabs(1.d0-u(1)))
36     &    -2.d0*u(1)/x
37!
38      return
39!
40      end
41!
42