Hi, Is there an easy way to gather all values of an IS across all processes in a communicator while removing duplicates? Basically, I want to go from [0] Number of indices in set 2 [0] 0 1 [0] 1 2 [1] Number of indices in set 2 [1] 0 2 [1] 1 3 to [0] Number of indices in set 3 [0] 0 1 [0] 1 2 [0] 2 3 [1] Number of indices in set 3 [1] 0 1 [1] 1 2 [1] 2 3 The way I do it right now is ierr = ISGetTotalIndices(csIS,&labels);CHKERRQ(ierr); ierr = ISGetSize(csIS,&num_cs_global);CHKERRQ(ierr); ierr = PetscMalloc(num_cs_global * sizeof(PetscInt),&labels2); for (i = 0; i < num_cs_global; i++) { labels2[i] = labels[i]; } ierr = PetscSortRemoveDupsInt(&num_cs_global,labels2);CHKERRQ(ierr); ierr = ISCreateGeneral(comm,num_cs_global,labels2,PETSC_COPY_VALUES,&csIS_global);CHKERRQ(ierr); ierr = ISRestoreTotalIndices(csIS,&labels);CHKERRQ(ierr); ierr = PetscFree(labels2);CHKERRQ(ierr); but there has to be a better way (or at least one that does not involve copying from const PetscInt *labels to PetscInt *labels2, and then uses again PETSC_COPY_VALUES). Blaise -- Department of Mathematics and Center for Computation & Technology Louisiana State University, Baton Rouge, LA 70803, USA Tel. +1 (225) 578 1612, Fax +1 (225) 578 4276 http://www.math.lsu.edu/~bourdin