[petsc-users] questions about the SNES Function Norm

[Barry Smith]

On Apr 28, 2014, at 3:23 PM, Xiangdong <epscodes at gmail.com> wrote:

> Hello everyone,
> 
> When I run snes program,

               ^^^^ what SNES program”?

> it outputs "SNES Function norm 1.23456789e+10". It seems that this norm is different from residue norm (even if solving F(x)=0)

   Please send the full output where you see this.

> and also differ from norm of the Jacobian. What is the definition of this "SNES Function Norm”?

   The SNES Function Norm as printed by PETSc is suppose to the 2-norm of F(x) - b (where b is usually zero) and this is also the same thing as the “residue norm” 

   Barry

> 
> Thank you.
> 
> Best,
> Xiangdong