How to get the residual vector after each nonlinear step

[tu1620808124]

Hello,
In every SNES step， there will return a residual norm. When I do the debugging, I want to get the residual vector. PETSc maybe uses the post-check function. How to get the residual vector in firedrake？

[wence-]

You can pass in a post_function_callback function to the nonlinear solver that gets given the residual after it is assembled.

You can also set a custom monitor on the snes with solver.snes.setMonitor with signature def monitor(snes, rnorm, its) (IIRC) and then use snes.getSolution to get the current guess, and snes.getFunction to get the function for computing the residual (you can then call that function on the current guess to get the residual/