How to initialize jexcel cell value

Question

I entered the formula in a specific cell. And I wrote a code to change the formula expression to setValue according to the value of the select box outside of jexcel. However, what was fast in the first formula was changed and it became slow. Formula expressions are slow even for simple expressions like '=A5'. So, I checked and the error message Reference loop detected is written to the console. So, thinking about it, if I use setValue, I think that the value is accumulated rather than changed. Is there any other way to initialize it?? The same problem occurs even if null is set to setValue before formula change.