global_matrix.m

function [A_Data] = global_matrix (pde, opts, hash_table)

% Global Matrix construction from the coefficient matricies coeffMat1 and
% coeffMat2 by looping over each grid point (i.e., elements of the hash).
% Each grid point is represented by a row in the global system matrix A,
% with the non-zero elements of that row being the other grid points to
% which the point is connected.

if opts.use_oldhash
    N = size(hash_table,2);
else
    Ne = numel(hash_table.elements_idx);
    N = Ne;
end
nDims = numel(pde.dimensions);

% Use tensor product encoding over deg.

dofCnt = 1;
conCnt = 1;

% Allocate element arrays

element_global_row_index  = zeros(N,1);

for d=1:nDims
    element_local_index_D{d} = zeros(N,1);
end
element_n_connected       = zeros(N,1);

for workItem = 1:N
    
    % Get the coordinates in the basis function space for myRow (this
    % element). (Lev1,Lev2,Cel1,Cel2,idx1D_1,idx1D_2) Lev1,Lev2,Cel1,Cel2
    % are NOT used here.
    
    if opts.use_oldhash
        thisRowBasisCoords = hash_table{workItem};
    else
    end
    
    % Get the 1D indexes into the [lev,pos] space for this element (row)
    
    for d=1:nDims
        
        if opts.use_oldhash
            element_idx1D_D{d} = thisRowBasisCoords(nDims*2+d);
        else
            IDlev = hash_table.elements.lev_p1(hash_table.elements_idx(workItem),d)-1;
            IDpos = hash_table.elements.pos_p1(hash_table.elements_idx(workItem),d)-1;
            IDe = lev_cell_to_1D_index(IDlev,IDpos);
            element_idx1D_D{d} = IDe;
        end
    end
    
    % Store the element data in arrays
    element_global_row_index(dofCnt) = workItem;
    
    for d=1:nDims
        element_local_index_D{d}(dofCnt) = element_idx1D_D{d};
    end
   
    dofCnt = dofCnt + 1;
    
end

% Wrap the arrays up into a struct just for ease of passing around.

A_Data.element_global_row_index = element_global_row_index;
A_Data.element_local_index_D = element_local_index_D;

end