function obj3 = binaryopp(f, obj1, obj2)

    if isa(obj2, 'mmo'), tmpobj = obj2; obj2 = obj1; obj1 = tmpobj; clear tmpobj; end

    if ~isequal(size(obj1), size(obj2)) && prod(size(obj2)) ~= 1

        error('Matrix dimensions must agree.');

    end

    data1 = memmapfile(obj1.dataFile, 'writable', obj1.writable, 'format', { 'single' obj1.dimensions 'x' });

    if isa(obj2, 'mmo'), 

         data2 = memmapfile(obj2.dataFile, 'writable', obj2.writable, 'format', { 'single' obj2.dimensions 'x' });

    else data2 = obj2;

    end

    % make new memory mapped data file (blank)

    % --------------------------------

    newFileName = mmo.getnewfilename;

    fid = fopen(newFileName, 'w');

    s1  = size(obj1);

    ss.type = '()';

    ss.subs(1:length(s1)-1) = { ':' };

    for index = 1:s1(end)

        ss.subs{length(s1)} = index;

        if prod(size(data2)) == 1

             tmpdata = f(subsref(data1.Data.x, ss), data2);

        else tmpdata = f(subsref(data1.Data.x, ss), subsref(data2.Data.x, ss));

        end

        fwrite(fid, tmpdata, 'float');

    end

    fclose(fid);    

    % create object

    % -------------

    obj3 = mmo(newFileName, s1, true, obj1.transposed);

    obj3 = updateWorkspace(obj3);