Plug PETSc's AMG preconditioner

src/algebra/LinearSolver.cpp

@@ -88,6 +88,7 @@ struct LinearSolver::Internals
   {
     switch (precond) {
     case LSPrecond::none:
+    case LSPrecond::amg:
     case LSPrecond::diagonal:
     case LSPrecond::incomplete_choleski:
     case LSPrecond::incomplete_LU: {
@@ -244,6 +245,10 @@ struct LinearSolver::Internals
 
     if (not direct_solver) {
       switch (options.precond()) {
+      case LSPrecond::amg: {
+        PCSetType(pc, PCGAMG);
+        break;
+      }
       case LSPrecond::diagonal: {
         PCSetType(pc, PCJACOBI);
         break;