Originally Posted by

**bearcat** Hello,

I am working on numerical solution of incompressible fluid dynamics problem. I need to compute the Jacobian of a viscous flux. I have to deduct some derivatives like this

$\displaystyle \frac{\partial (\frac{\partial U}{\partial x})}{\partial U}=?$

Some people say the result is absolutely not zero, but I still could not find an analytical answer. I wonder this will turn out into a derivative operator rather than an expression of fixed value. If an analytical expression is not possible, how to handle this in a finite difference method?

Thank you and have a good day!

Bearcat