  function ut=pde_1(t,u)
%
% Parameters
  global xl xu nx ncall ndss ncase
%
% BC at x = 0 (Dirichlet)
  u(1)=1;
%
% ux
  if    (ndss== 2) ux=dss002(xl,xu,nx,u); % second order  
  elseif(ndss== 4) ux=dss004(xl,xu,nx,u); % fourth order
  elseif(ndss== 6) ux=dss006(xl,xu,nx,u); % sixth order
  elseif(ndss== 8) ux=dss008(xl,xu,nx,u); % eighth order      
  elseif(ndss==10) ux=dss010(xl,xu,nx,u); % tenth order
  end     
%
% BC at x = 1 (Neumann)
  ux(nx)=0;
%
% Diffusivity
  for i=1:nx
    if(ncase==1)D(i)=1        ;end
    if(ncase==2)D(i)=u(i)     ;end
    if(ncase==3)D(i)=exp(u(i));end
    ux(i)=D(i)*ux(i);
  end   
%
% uxx
  if    (ndss== 2) uxx=dss002(xl,xu,nx,ux); % second order  
  elseif(ndss== 4) uxx=dss004(xl,xu,nx,ux); % fourth order
  elseif(ndss== 6) uxx=dss006(xl,xu,nx,ux); % sixth order
  elseif(ndss== 8) uxx=dss008(xl,xu,nx,ux); % eighth order      
  elseif(ndss==10) uxx=dss010(xl,xu,nx,ux); % tenth order
  end     
%
% PDE
  ut=uxx';
  ut(1)=0;
%
% Increment calls to pde_1
  ncall=ncall+1;

