Thank you. I will try to divide the ring into fragments and see what happens.
Michael. On 9/7/2019 5:15 AM, Jose E. Roman wrote: > In the ring region, you should choose appropriate start and end angles to > narrow down the region, so that it fits closer to the wanted eigenvalues, > otherwise the region spans the whole circumference. Note that there is a > fixed number of integration points around the contour, so if the area is not > focused around the wanted eigenvalues then the approximation capacity is > smaller. > > As I said, elliptic regions are mostly recommended. The ring region is used > for special situations, such as the one in our joint paper > https://doi.org/10.1007/978-3-319-62426-6_2 where the eigenvalues lie on the > unit circle but we want to avoid eigenvalues close to the origin. > > Jose > > >> El 6 sept 2019, a las 22:11, Povolotskyi, Mykhailo via petsc-users >> <[email protected]> escribió: >> >> Hello, >> >> I have been experimenting with CISS by computing part of the spectrum of >> a complex matrix of rather small size (774). >> >> I have compared two spectral regions: the circle and the ring. >> >> The results were compared against LAPACK. >> >> The attached figure shows that the accuracy with the ring is low, >> comparatively to a circle. >> >> It looks like if the ring is used, the eigenvalues are found, but not >> accurately. >> >> The circle area works quite okay. >> >> This is what I'm doing: >> >> EPS eps; >> EPSType type; >> RG rg; >> >> EPSCreate(MPI_COMM_SELF,&eps); >> EPSSetOperators( eps,matrix_petsc,NULL); >> EPSSetType(eps,EPSCISS); >> EPSSetProblemType(eps, EPS_NHEP); >> >> EPSSetFromOptions(eps); >> >> >> EPSGetRG(eps,&rg); >> RGSetType(rg,RGRING); >> >> double vscale(1.0); >> >> double start_ang(0); >> double end_ang(1.0); >> RGRingSetParameters(rg,center,radius,vscale,start_ang,end_ang,width); >> >> EPSSolve(eps); >> >> >> Could you, please, advise me on this problem? >> >> Thank you, >> >> Michael. >> >> <circle_vs_ring2.png>
