Hello, I use KSP and random rhs to compute largest singular value: ! create solver and set options for singular value estimation call KSPCreate(MPI_COMM_WORLD,ksp,ierr);CHKERRQ(ierr) call KSPSetType(ksp,KSPGMRES,ierr);CHKERRQ(ierr) call KSPSetTolerances(ksp,solvertol,PETSC_DEFAULT_DOUBLE_PRECISION,PETSC_DEFAULT_DOUBLE_PRECISION,its,ierr);CHKERRQ(ierr) call KSPGMRESSetRestart(ksp, its, ierr);CHKERRQ(ierr) call KSPSetComputeSingularValues(ksp, flg, ierr);CHKERRQ(ierr) call KSPSetFromOptions(ksp,ierr);CHKERRQ(ierr) ! generate random RHS call PetscRandomCreate(PETSC_COMM_WORLD,rctx,ierr) call PetscRandomSetFromOptions(rctx,ierr) call VecSetRandom(b,rctx,ierr) !no preconditioning call KSPGetPC(ksp,pc,ierr);CHKERRQ(ierr) call PCSetType(pc,PCNONE,ierr);CHKERRQ(ierr) call KSPSetOperators(ksp,A,A,SAME_PRECONDITIONER,ierr);CHKERRQ(ierr) !solve system call KSPSolve(ksp,b,x,ierr);CHKERRQ(ierr) call KSPComputeExtremeSingularValues(ksp, smax, smin, ierr);CHKERRQ(ierr) call KSPDestroy(ksp,ierr);CHKERRQ(ierr) However it crashes: [1]PETSC ERROR: ------------------------------------------------------------------------ [1]PETSC ERROR: Caught signal number 11 SEGV: Segmentation Violation, probably memory access out of range [1]PETSC ERROR: Try option -start_in_debugger or -on_error_attach_debugger [1]PETSC ERROR: or see http://www.mcs.anl.gov/petsc/documentation/faq.html#valgrind[1]PETSC ERROR: or try http://valgrind.org on GNU/linux and Apple Mac OS X to find memory corruption errors [1]PETSC ERROR: PetscMallocValidate: error detected at PetscDefaultSignalHandler() line 157 in /home/lib/petsc-dev1/src/sys/error/signal.c [1]PETSC ERROR: Memory at address 0x4aa3f00 is corrupted [1]PETSC ERROR: Probably write past beginning or end of array [1]PETSC ERROR: Last intact block allocated in KSPSetUp_GMRES() line 73 in /home/lib/petsc-dev1/src/ksp/ksp/impls/gmres/gmres.c [1]PETSC ERROR: --------------------- Error Message ------------------------------------ [1]PETSC ERROR: Memory corruption! [1]PETSC ERROR: ! [1]PETSC ERROR: ------------------------------------------------------------------------ [1]PETSC ERROR: Petsc Development HG revision: f3c119f7ddbfee243b51907a90acab15127ccb39 HG Date: Sun Apr 29 21:37:29 2012 -0500 [1]PETSC ERROR: See docs/changes/index.html for recent updates. [1]PETSC ERROR: See docs/faq.html for hints about trouble shooting. [1]PETSC ERROR: See docs/index.html for manual pages. [1]PETSC ERROR: ------------------------------------------------------------------------ [1]PETSC ERROR: /home/prog on a openmpi-i named node207 by user Sun May 6 12:58:24 2012 [1]PETSC ERROR: Libraries linked from /home/lib/petsc-dev1/openmpi-intel-complex-debug-f/lib [1]PETSC ERROR: Configure run at Mon Apr 30 10:20:49 2012 [1]PETSC ERROR: Configure options --with-blacs-include=/opt/intel/Compiler/11.1/072/mkl/include --with-blacs-lib=/opt/intel/Compiler/11.1/072/mkl/lib/em64t/libmkl_blacs_openmpi_lp64.a --with-blas-lapack-lib="[/opt/intel/Compiler/11.1/072/mkl/lib/em64t/libmkl_intel_lp64.a,/opt/intel/Compiler/11.1/072/mkl/lib/em64t/libmkl_intel_thread.a,/opt/intel/Compiler/11.1/072/mkl/lib/em64t/libmkl_core.a,/opt/intel/Compiler/11.1/072/lib/intel64/libiomp5.a]" --with-fortran-interfaces=1 --with-mpi-dir=/opt/mpi/intel/openmpi-1.4.2 --with-petsc-arch=openmpi-intel-complex-debug-f --with-precision=double --with-scalapack-include=/opt/intel/Compiler/11.1/072/mkl/include --with-scalapack-lib=/opt/intel/Compiler/11.1/072/mkl/lib/em64t/libmkl_scalapack_lp64.a --with-scalar-type=complex --with-x=0 PETSC_ARCH=openmpi-intel-complex-debug-f [1]PETSC ERROR: ------------------------------------------------------------------------ [1]PETSC ERROR: PetscMallocValidate() line 138 in /home/lib/petsc-dev1/src/sys/memory/mtr.c [1]PETSC ERROR: PetscDefaultSignalHandler() line 157 in /home/lib/petsc-dev1/src/sys/error/signal.c Call stack from debugger: opal_memory_ptmalloc2_int_free, FP=7fffd4765300 opal_memory_ptmalloc2_free_hook, FP=7fffd4765330 PetscFreeAlign, FP=7fffd4765370 PetscTrFreeDefault, FP=7fffd4765520 KSPReset_GMRES, FP=7fffd4765740 KSPReset, FP=7fffd4765840 KSPDestroy, FP=7fffd47659a0 kspdestroy_, FP=7fffd47659d0 Any ideas? Thanks. -- Regards, Alexander