function step_domain
%step_domain   standard L-shaped domain Q2 grid generator
%   step_domain;
% 
% Neumann boundary condition on right-hand edge
% grid defining data is saved to the file: step_grid.mat
%   IFISS function: DJS; 7 May 2006.
% Copyright (c) 2005 D.J. Silvester, H.C. Elman, A. Ramage 
clear 
fprintf('\n\nGrid generation for a step shaped domain.\n')
nc=default('grid parameter: 3 for underlying 8x24 grid (default is 4)',4);
if nc<2, error('illegal parameter choice, try again.'), end
%stretch=default('grid stretch factor (default is 1)',1);
stretch=1;
n=2^nc; np=n/2; nq=n/4;
ny=n;nx=3*n; 
%
%% compute (x,y) coordinates of vertices
% y-direction
if stretch >1
   dy=(1-stretch)/(1-stretch^np);
   yy(1)=dy;
   for k=1:np-1, yy(k+1)=yy(k)+dy*stretch^k; end
   yy(np)=1;
   else
   yy=[1/np:1/np:1];
   end
ypos=[0,yy];
yneg=-yy(length(yy):-1:1);
y=[yneg,ypos];
% x-direction
xx=yneg;
xneg=[xx];
xpos=[0:1/np:5];
x=[xneg,xpos];
%
%% compute biquadratic element coordinates
nvtx= np*(np+1) + (5*np+1)*(n+1);
% negative x-values
[Xneg,Ypos]=meshgrid(xneg,ypos);
xx=reshape(Xneg',np*(np+1),1);
yy=reshape(Ypos',np*(np+1),1);
xyleft=[xx(:),yy(:)];
kx = 1;
ky = 1;
mel=0;
% symbolic assembly 
% loop over 2x2 macroelements
for j=1:nq
for i=1:nq
mref=np*(ky-1)+kx;
mel=mel+1;
nvv(1) = mref;
nvv(2) = mref+2;
nvv(3) = mref+2*np+2;
nvv(4) = mref+2*np;
nvv(5) = mref+1;
nvv(6) = mref+np+2; 
nvv(7) = mref+2*np+1; 
nvv(8)=  mref+np;
nvv(9)=  mref+np+1; 
mv(mel,1:9)=nvv(1:9);
kx = kx + 2;
end
ky = ky + 2;
kx = 1;
end
% correction along the internal boundary
mref=2*np*(3*np+1)+1;
for mel=nq:nq:nq*nq;
nvv=mv(mel,:);
nvv(2) = mref;
nvv(3) = mref+10*np+2;
nvv(6) = mref+5*np+1; 
mv(mel,1:9)=nvv(1:9);
mref=mref+10*np+2;
end	
%
% positive x_values
[Xpos,Y]=meshgrid(xpos,y);
xx=reshape(Xpos',(5*np+1)*(n+1),1);
yy=reshape(Y',(5*np+1)*(n+1),1);
xyright=[xx(:),yy(:)];
xy=[xyleft;xyright]; 
%
kx = 1;
ky = 1;
mel=nq*nq;
for j=1:np
for i=1:5*nq
mref = (5*np+1)*(ky-1)+kx + np*(np+1);
mel=mel+1;
nvv(1) = mref;
nvv(2) = mref+2;
nvv(3) = mref+10*np+4;
nvv(4) = mref+10*np+2;
nvv(5) = mref+1;
nvv(6) = mref+5*np+3; 
nvv(7) = mref+10*np+3; 
nvv(8)=  mref+5*np+1;
nvv(9)=  mref+5*np+2; 
mv(mel,1:9)=nvv(1:9);
kx = kx + 2;
end
ky = ky + 2;
kx = 1;
end
%
%% compute boundary vertices
% six boundary edges 
k1=find( xy(:,1) <0  & xy(:,2)==0 );
e1=[]; for k=1:mel, if any(mv(k,5)==k1), e1=[e1,k]; end, end
ef1=ones(size(e1));
%
k2=find( xy(:,1)==0  & xy(:,2)<=0 );
e2=[]; for k=1:mel, if any(mv(k,8)==k2), e2=[e2,k]; end, end
ef2=4*ones(size(e2));
%
k3=find( xy(:,1) >0  & xy(:,2)==-1);
e3=[]; for k=1:mel, if any(mv(k,5)==k3), e3=[e3,k]; end, end
ef3=ones(size(e3));
%
%
k5=find( xy(:,2)==1 );
e5=[]; for k=1:mel, if any(mv(k,7)==k5), e5=[e5,k]; end, end
ef5=3*ones(size(e5));
%
k6=find( xy(:,1)==-1 & xy(:,2)<1   & xy(:,2) >0 );
e6=[]; for k=1:mel, if any(mv(k,8)==k6), e6=[e6,k]; end, end
ef6=4*ones(size(e6));
%
bound=sort([k1;k2;k3;k5;k6]);
mbound=[e1',ef1';e2',ef2';e3',ef3';;e5',ef5';e6',ef6'];
%
% 
%%
gohome 
cd datafiles
save step_grid.mat mv xy bound mbound stretch x y
clear 
return