MatMarket/mmread.m

function  [A,rows,cols,entries,rep,field,symm] = mmread(filename)
%
% function  [A] = mmread(filename)
%
% function  [A,rows,cols,entries,rep,field,symm] = mmread(filename)
%
%      Reads the contents of the Matrix Market file 'filename'
%      into the matrix 'A'.  'A' will be either sparse or full,
%      depending on the Matrix Market format indicated by
%      'coordinate' (coordinate sparse storage), or
%      'array' (dense array storage).  The data will be duplicated
%      as appropriate if symmetry is indicated in the header.
%
%      Optionally, size information about the matrix can be 
%      obtained by using the return values rows, cols, and
%      entries, where entries is the number of nonzero entries
%      in the final matrix. Type information can also be retrieved
%      using the optional return values rep (representation), field,
%      and symm (symmetry).
%

mmfile = fopen(filename,'r');
if ( mmfile == -1 )
 disp(filename);
 error('File not found');
end;

header = fgets(mmfile);
if (header == -1 )
  error('Empty file.')
end

% NOTE: If using a version of Matlab for which strtok is not
%       defined, substitute 'gettok' for 'strtok' in the 
%       following lines, and download gettok.m from the
%       Matrix Market site.    
[head0, header]   = strtok(header);  % see note above
[head1, header]   = strtok(header);
[rep, header]     = strtok(header);
[field, header]   = strtok(header);
[symm, header]    = strtok(header);
head1 = lower(head1);
rep   = lower(rep);
field = lower(field);
symm  = lower(symm);
if isempty(symm)
   disp(['Not enough words in header line of file ',filename]) 
   disp('Recognized format: ')
   disp('%%MatrixMarket matrix representation field symmetry')
   error('Check header line.')
end
if ~strcmp(head0,'%%MatrixMarket')
   error('Not a valid MatrixMarket header.')
end
if ~strcmp(head1,'matrix')
   disp(['This seems to be a MatrixMarket ',head1,' file.']);
   disp('This function only knows how to read MatrixMarket matrix files.');
   disp('  ');
   error('  ');
end

% Read through comments, ignoring them
commentline = fgets(mmfile);
while ~isempty(commentline) && commentline(1) == '%',
	commentline = fgets(mmfile);
end

% Read size information, then branch according to
% sparse or dense format

switch rep,
    case 'coordinate', % read matrix given in sparse coordinate format
        [sizeinfo,count] = sscanf(commentline, '%d%d%d');
        while count == 0,
            commentline =  fgets(mmfile);
            if commentline == -1,
                error('End-of-file reached before size information was found.')
            end
            [sizeinfo,count] = sscanf(commentline, '%d%d%d');
            if count > 0 && count ~= 3,
                error('Invalid size specification line.')
            end
        end
        rows = sizeinfo(1);
        cols = sizeinfo(2);
        entries = sizeinfo(3);

        T = fscanf(mmfile, '%f');
        switch field,                        
            case 'real',         % real valued entries:
                check_size(T, 3 * entries);
                T = reshape(T(:), 3, entries)';
                A = sparse(T(:,1), T(:,2), T(:,3), rows , cols);
            case 'complex',   % complex valued entries:
                check_size(T, 4 * entries);
                T = reshape(T(:), 4, entries)';
                A = sparse(T(:,1), T(:,2), T(:,3) + T(:,4)*1i, rows , cols);
            case 'pattern',  % pattern matrix (no values given):
                check_size(T, 2 * entries);
                T = reshape(T(:), 2, entries)';
                A = sparse(T(:,1), T(:,2), ones(entries, 1), rows , cols);
        end
    case 'array', % read matrix given in dense array (column major) format
        [sizeinfo, count] = sscanf(commentline, '%d%d');
        while count == 0
            commentline = fgets(mmfile);
            if commentline == -1
                error('End-of-file reached before size information was found.')
            end
            [sizeinfo, count] = sscanf(commentline, '%d%d');
            if count > 0 && count ~= 2
                error('Invalid size specification line.')
            end
        end
        rows = sizeinfo(1);
        cols = sizeinfo(2);
        entries = rows*cols;
        
        A = fscanf(mmfile, '%f');
        switch field,
            case 'real',                        % real valued entries:
                % do nothing
            case 'complex',                     % complex valued entries:
                A = A(1:2:end-1) + 1i * A(2:2:end);
            case 'pattern',  % pattern (makes no sense for dense)
                disp('Matrix type:',field)
                error('Pattern matrix type invalid for array storage format.');
            otherwise,
                disp('Matrix type:',field)
                error('Invalid matrix type specification. Check header against MM documentation.');
        end
        if any(strcmp(symm,{'symmetric','hermitian','skew-symmetric'}))
            for j=1:cols-1,
                currenti = j*rows;
                A = [A(1:currenti); 
                     zeros(j,1);
                     A(currenti+1:length(A))];
            end
        elseif ~strcmp(symm,'general'),
            disp('Unrecognized symmetry')
            disp(symm)
            disp('Recognized choices:')
            disp('   symmetric')
            disp('   hermitian')
            disp('   skew-symmetric')
            disp('   general')
            error('Check symmetry specification in header.');
        end
        A = reshape(A,rows,cols);
end

fclose(mmfile);

%
% If symmetric, skew-symmetric or Hermitian, duplicate lower
% triangular part and modify entries as appropriate:
%

switch symm,
    case 'symmetric',
       A = A + A.' - diag(diag(A));
       entries = nnz(A);
    case 'hermitian',
        A = A + A' - diag(diag(A));
        entries = nnz(A);
    case 'skew-symmetric',
        A = A - A.';
        entries = nnz(A);
end
% Done.

end


function check_size(T, n)
    if size(T) ~= n
       disp('Data file does not contain expected amount of data.');
       disp('Check that number of data lines matches nonzero count.');
       error('Invalid data.');
    end
end