Update field using value of another field

Hello mongodb team

I need to do a bulk update, I need to pass the value of one field to another and multiply it by a factor.

I have read the other questions but I did not see an answer to the problem that I expose.

Is this possible?

This is a very simple code:

                    required_kvar : "$kw_base"      // this not work


The update operator $set is to set the value of a field. If you want to

you need $mul.