function  fwrite_mx(fname,matrix)
% writes mx matrix with header in bin format. 
%  Fwrite of Matlab writes the data in COLUMN order, therefore we transpose
%  before the writing. 
no_rows = size(matrix,1);
no_cols = size(matrix,2);

fid = fopen(fname,'w');
header = strcat('<',num2str(no_rows),'> <',num2str(no_cols),'>');
fprintf(fid,'%s\n',header);
fwrite(fid,matrix','float');
fclose(fid);