--- a
+++ b/functions/@mmo/binaryopp.m
@@ -0,0 +1,33 @@
+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);