isoc

 Generates pdetoolbox c-tensor for the isotropic case
 1. cij12=cij21=0 (no (x,y)-mixed derivative terms) 
 2. cij11=cij22 (isotropic diffusion)
 Hence, c is only a N-by-N tensor, where the i-th component of 
 grad(c tensor grad u) is div(divmat_i dot grad u),
 where divmat_i ist i-th row of divmat.

  divmat is a neq-by-neq matrix of vectors with nt components
  In particular, if diffusion/fluxes are space-independent then use
  nt=1 and divmat an neq-by-neq matrix.

0001 function c=isoc(divmat,neq,nt)
0002 % Generates pdetoolbox c-tensor for the isotropic case
0003 % 1. cij12=cij21=0 (no (x,y)-mixed derivative terms)
0004 % 2. cij11=cij22 (isotropic diffusion)
0005 % Hence, c is only a N-by-N tensor, where the i-th component of
0006 % grad(c tensor grad u) is div(divmat_i dot grad u),
0007 % where divmat_i ist i-th row of divmat.
0008 %
0009 %  divmat is a neq-by-neq matrix of vectors with nt components
0010 %  In particular, if diffusion/fluxes are space-independent then use
0011 %  nt=1 and divmat an neq-by-neq matrix.
0012 
0013 c=[];
0014 dz=zeros(1,nt);
0015 for j=0:neq-1
0016     for i=1:neq
0017         cij11=divmat(i,1+j*nt:(j+1)*nt);
0018         cij22=cij11;
0019         cij12=dz;
0020         cij21=dz;
0021         c=[c;cij11;cij21;cij12;cij22];
0022     end
0023 end
0024 
0025 % ordering example: (3 compo system, i.e. 4*9=36 entries in c)
0026 %c=[c1111; c1121; c1112; c1122; c2111; c2121; c2112; c2122; ...
0027 %   c3111; c3121; c3112; c3122; ...
0028 %   c1211; c1221; c1212; c1222; c2211; c2221; c2212; c2222;...
0029 %   c3211; c3221; c3212; c3222; ...
0030 %   c1311; c1321; c1312; c1322; c2311; c2321; c2312; c2322;...
0031 %   c3311; c3321; c3312; c3322];