Hi Nasser, > But my question is: Why \newcommand inside Latex had no effect > when compiling to mathjax but it work in SVG?
Because the \newcommand isn't included in HTML so MathJax cannot see it. Moreover, it is quite possible that you will need different command declarations for LaTeX and MathJax. In the SVG mode, part of rendered DVI file is converted to image, the DVI file contains result of full macro expansion, so it doesn't suffer from such issues. MathML output also contains all commands expanded. Best, Michal
