On Mon, Nov 11, 2013 at 12:03 PM, Qiyue Lu <[email protected]> wrote:
> 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 > The residual r for some approximate solution x is r = b - Ax The initial residual uses the initial guess, often 0. Matt > > > 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 >> > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
