Migration Procedure

Migrating the Library That Uses the C Language

Both PETSc and KML_SCASOLVER provide C interfaces. However, the interface names and receiving parameters are inconsistent. Therefore, the corresponding function needs to be switched. The following are examples:

1. Initialization
   Before the migration:

   KSP            ksp;
   PetscErrorCode ierr;
   ierr = KSPCreate(PETSC_COMM_WORLD,&ksp);
   ierr = KSPSetOperators(ksp,A,A);

   After the migration:

   int n = 8; 
   int nstripes = 1;
   int stripeWidth[1]; 
   int stripeRow[1];
   int ia[9];
   int ja[17];
   double a[17];
   KmlScasolverTask* handle; 
   int err;
   err = KmlScaissCgInitStripesDI(&handle, n, nstripes , stripeWidth, stripeRow, a, ja, ia, MPI_COMM_WORLD); 

2. Setting parameters for finding the solution
   Before the migration:

   ierr = KSPSetTolerances(ksp,1e-4,PETSC_DEFAULT,PETSC_DEFAULT,2000);

   After the migration:

   double eps = 1e-4;
   err = KmlScaissCgSetDID(&handle, KMLSS_THRESHOLD, &eps, 1); assert(err == 0);
   int max_iters = 2000;
   err = KmlScaissCgSetDII(&handle, KMLSS_MAX_ITERATION_COUNT, &max_iters, 1);

3. Finding the solution
   Before the migration:

   Vec            u,x,b;
   ierr = VecCreate(PETSC_COMM_WORLD,&u);
   ierr = VecSetSizes(u,PETSC_DECIDE,rdim);
   ierr = VecSetFromOptions(u);CHKERRQ(ierr);
   ierr = VecDuplicate(u,&b);CHKERRQ(ierr);
   ierr = VecDuplicate(b,&x);CHKERRQ(ierr);
   
   ierr = KSPSolve(ksp,b,x);CHKERRQ(ierr);

   After the migration:

   int nb=1;
   double* x[8];
   double* b[8];
   int ldx=4;
   int ldb=4;
   err = KmlScaissCgSolveDI(&handle, nb, x, ldx, b, ldb);

4. Obtaining iteration parameters
   Before the migration:

   PetscInt       its;
   PetscScalar      norm;
   ierr = KSPGetIterationNumber(ksp,&its);CHKERRQ(ierr);
   ierr = KSPGetResidualNorm(ksp,&norm);CHKERRQ(ierr);

   After the migration:

   int idata[] = {max_iters};
   err = KmlScaissCgGetDII(&handle, KMLSS_ITERATION_COUNT, data, 1); 
   double ddata[] = {eps};
   err = KmlScaissCgGetDID(&handle, KMLSS_TOLERANCE, ddata, 1);

5. Clearing
   Before the migration:

   ierr = KSPDestroy(&ksp);

   After the migration:

   err = KmlScaissCgCleanDI(&handle);

6. Header file

   Before the migration:

   #include "petscksp.h"

   After the migration:

   #include "kml_scaiss.h"

7. Compiling the links

   Replace the link options related to PETSc. For details, see "Installing KML > Verifying the Installation" in Kunpeng Math Library Developer Guide.