Sorry, I made a mistake in privous email. in my output file, the *KSP residual norm* not the rtol is 1.0e-4 at the 1st iteration. My question is how this residual norm calculated? Is there any initial guess there? thanks
On Mon, Nov 11, 2013 at 11:55 AM, Qiyue Lu <[email protected]> wrote: > Dear All: > > I am working on a linear A*x=b system. > When I use *-ksp_rtol 1.0e-5 *option in the command line, I am not very > sure how the relative tolerance is defined. > > In my understanding: > > At the beginning, r= b-A*x_i, so rtol = ||r|| / ||b|| with 2-norm has a > value. with the calculation, rtol gets smaller, when the rtol_new / > rtol_original < 1.0e-5, the calculation will stop. > > Is my understanding correct? > > If so, how to decide the rtol at the first iteration? If initial solution > values are all zeros, then rtol should be 1.0. In my output file, it's a > value related to the matrix and can be at 1.0e-4 scale. Is there any > initial guess solution from preconditioner used there? > > Could you help to clarify this definition? Thanks > > > Qiyue Lu >
