gnbcs

 generalized Neumann BC: generate q,g, string allowed
 even length varargin:
   varargin is vector of edgenum pairs (q,g), with one pair per edge 
   of the domain.
 odd length varargin for equal (q,g) on each edge:
   varargin = (edgenum, q, g)
    
 Returns a boundary matrix for a system with pneq components on a domain 
 with generalized Neumann bc per egde given by (q,g) of the form  
                    n*c tensor grad(u) + q*u = g,
 where q is an pneq by pneq matrix and g a vector with pneq components. 
 Both contain strings that may be formulas in terms of u, x, t etc.

0001 function bc= gnbcs(pneq,varargin)
0002 % generalized Neumann BC: generate q,g, string allowed
0003 % even length varargin:
0004 %   varargin is vector of edgenum pairs (q,g), with one pair per edge
0005 %   of the domain.
0006 % odd length varargin for equal (q,g) on each edge:
0007 %   varargin = (edgenum, q, g)
0008 %
0009 % Returns a boundary matrix for a system with pneq components on a domain
0010 % with generalized Neumann bc per egde given by (q,g) of the form
0011 %                    n*c tensor grad(u) + q*u = g,
0012 % where q is an pneq by pneq matrix and g a vector with pneq components.
0013 % Both contain strings that may be formulas in terms of u, x, t etc.
0014 
0015 % Note: q = [[12;6789];[345;101112]] means q21=6789 in PDEtool GUI.
0016 
0017 if(mod(length(varargin),2)==0) 
0018     edgenum = length(varargin)/2;
0019 else
0020     edgenum = varargin{1};
0021     if(length(varargin)~=3) 
0022         error('argument list has wrong length')
0023     end
0024     q = varargin{2};
0025     g = varargin{3};
0026     for jj=1:edgenum
0027         varargin{2*jj-1} = q;
0028         varargin{2*jj}   = g;
0029     end
0030 end
0031 
0032 bb(1,:)= pneq*ones(edgenum,1); % # of components
0033 bb(2,:)= zeros(edgenum,1); % set # Dirichlet b.c. to zero
0034 
0035 for jj=1:edgenum,
0036     q = varargin{2*jj-1};
0037     g = varargin{2*jj};
0038     % Add lengths of entries of q and g to bb
0039 
0040     % generate vector of entries of matrix q (analogue of  qa=q(:) )
0041     if pneq==1; qa{1}=q; else
0042         for ik=1:pneq;for ij=1:pneq
0043            qa{ij+pneq*(ik-1)}=q{ij}{ik};
0044     end; end; end
0045     for j=1:length(qa)
0046         qs=qa{j};
0047         bb(j+2,jj)=length(qs);
0048         qc = uint8(qs); % ascii codes of characters as vector
0049         bq{j} = qc; 
0050     end
0051 
0052     if pneq==1; ga{1}=g; else
0053         ga=g;
0054     end
0055     for j=1:length(ga)
0056         gs=ga{j};
0057         bb(j+2+length(qa),jj)=length(gs);
0058         gc = uint8(gs); % ascii codes of characters as vector
0059         bg{j} = gc(:);
0060     end
0061 
0062     % Add ascii codes of characters of entries to bb
0063 
0064     bcount = 0;
0065     for j=1:length(qa),
0066         bbq = bq{j};
0067         for k=1:length(bbq)
0068             bb(k+2+length(qa)+length(ga)+bcount,jj) = bbq(k);
0069         end
0070         bcount = bcount + length(bbq);
0071     end
0072 
0073     for j=1:length(ga),
0074         bbg = bg{j};
0075         for k=1:length(bbg)
0076             bb(k+2+length(qa)+length(ga)+bcount,jj) = bbg(k);
0077         end
0078         bcount = bcount + length(bbg);
0079     end
0080 
0081     bc=bb; % return bb
0082 end