Lisandro Dalcin avatar Lisandro Dalcin committed ee7de47

Code for Anders Logg's challenge in Google+

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Files changed (2)

demo/LoggChallenge.c

+#include "petiga.h"
+
+/*
+
+Solve the partial diferential equation
+
+   -Laplacian(u) = f
+
+with homogeneous Dirichlet boundary conditions on the unit square for
+
+   f(x,y) = 2 pi^2 sin(pi*x) * sin(pi*y).
+
++ Who can obtain the smallest error?
++ Who can compute a solution with an error smaller than 10^-6?
+
+*/
+
+PetscReal Forcing(PetscReal x, PetscReal y)
+{
+  PetscReal pi = M_PI;
+  return 2*pi*pi * sin(pi*x) * sin(pi*y);
+}
+
+#undef  __FUNCT__
+#define __FUNCT__ "System"
+PetscErrorCode System(IGAPoint p,PetscScalar *K,PetscScalar *F,void *ctx)
+{
+  PetscReal x = p->point[0];
+  PetscReal y = p->point[1];
+  PetscReal *N0 = p->shape[0];
+  PetscReal (*N1)[2] = (PetscReal (*)[2]) p->shape[1];
+  PetscInt a,b,nen=p->nen;
+  for (a=0; a<nen; a++) {
+    PetscReal Na   = N0[a];
+    PetscReal Na_x = N1[a][0];
+    PetscReal Na_y = N1[a][1];
+    for (b=0; b<nen; b++) {
+      PetscReal Nb_x = N1[b][0];
+      PetscReal Nb_y = N1[b][1];
+      K[a*nen+b] = Na_x*Nb_x + Na_y*Nb_y;
+    }
+    F[a] = Na * Forcing(x,y);
+  }
+  return 0;
+}
+
+PetscReal Exact(PetscReal x, PetscReal y)
+{
+  PetscReal pi = M_PI;
+  return sin(pi*x) * sin(pi*y);
+}
+
+#undef  __FUNCT__
+#define __FUNCT__ "Error"
+PetscErrorCode Error(IGAPoint p,const PetscScalar *U,PetscInt n,PetscScalar *S,void *ctx)
+{
+  PetscReal x = p->point[0];
+  PetscReal y = p->point[1];
+  PetscReal u_exact = Exact(x,y);
+  PetscScalar u;
+  IGAPointFormValue(p,U,&u);
+  PetscReal e = PetscAbsScalar(u - u_exact);
+  S[0] = e*e;
+  return 0;
+}
+
+#undef __FUNCT__
+#define __FUNCT__ "main"
+int main(int argc, char *argv[]) {
+
+  PetscErrorCode  ierr;
+  ierr = PetscInitialize(&argc,&argv,0,0);CHKERRQ(ierr);
+
+  PetscLogDouble tic,toc;
+  ierr = PetscGetTime(&tic);
+
+  IGA iga;
+  ierr = IGACreate(PETSC_COMM_WORLD,&iga);CHKERRQ(ierr);
+  ierr = IGASetDim(iga,2);CHKERRQ(ierr);
+  ierr = IGASetDof(iga,1);CHKERRQ(ierr);
+
+  IGABoundary bnd;
+  PetscInt dir,side;
+  for (dir=0; dir<2; dir++) {
+    for (side=0; side<2; side++) {
+      ierr = IGAGetBoundary(iga,dir,side,&bnd);CHKERRQ(ierr);
+      ierr = IGABoundarySetValue(bnd,0,0.0);CHKERRQ(ierr);
+    }
+  }
+
+  ierr = IGASetFromOptions(iga);CHKERRQ(ierr);
+  ierr = IGASetUp(iga);CHKERRQ(ierr);
+
+  Mat A;
+  Vec x,b;
+  ierr = IGACreateMat(iga,&A);CHKERRQ(ierr);
+  ierr = IGACreateVec(iga,&x);CHKERRQ(ierr);
+  ierr = IGACreateVec(iga,&b);CHKERRQ(ierr);
+  ierr = IGASetUserSystem(iga,System,PETSC_NULL);CHKERRQ(ierr);
+
+  PetscLogDouble ta1,ta2,ta;
+  ierr = PetscGetTime(&ta1);
+  ierr = IGAComputeSystem(iga,A,b);CHKERRQ(ierr);
+  ierr = PetscGetTime(&ta2);
+  ta = ta2-ta1;
+
+  KSP ksp;
+  ierr = IGACreateKSP(iga,&ksp);CHKERRQ(ierr);
+  ierr = KSPSetOperators(ksp,A,A,SAME_NONZERO_PATTERN);CHKERRQ(ierr);
+  ierr = KSPSetFromOptions(ksp);CHKERRQ(ierr);
+
+  PetscLogDouble ts1,ts2,ts;
+  ierr = PetscGetTime(&ts1);
+  ierr = KSPSolve(ksp,b,x);CHKERRQ(ierr);
+  ierr = PetscGetTime(&ts2);
+  ts = ts2-ts1;
+
+  ierr = PetscGetTime(&toc);
+  PetscLogDouble tt = toc-tic;
+
+  Vec r;
+  PetscReal rnorm;
+  ierr = VecDuplicate(b,&r);CHKERRQ(ierr);
+  ierr = MatMult(A,x,r);CHKERRQ(ierr);
+  ierr = VecAYPX(r,-1.0,b);CHKERRQ(ierr);
+  ierr = VecNorm(r,NORM_2,&rnorm);CHKERRQ(ierr);
+  ierr = VecDestroy(&r);CHKERRQ(ierr);
+
+  PetscInt its;
+  ierr = KSPGetIterationNumber(ksp,&its);CHKERRQ(ierr);
+
+  ierr = IGAReset(iga);CHKERRQ(ierr);
+  for (dir=0; dir<2; dir++) {
+    IGARule rule;
+    ierr = IGAGetRule(iga,dir,&rule);CHKERRQ(ierr);
+    ierr = IGARuleInit(rule,9);CHKERRQ(ierr);
+  }
+  ierr = IGASetUp(iga);CHKERRQ(ierr);
+
+  PetscScalar error = 0;
+  ierr = IGAFormScalar(iga,x,1,&error,Error,PETSC_NULL);CHKERRQ(ierr);
+  error = PetscSqrtReal(PetscRealPart(error));
+
+  ierr = PetscPrintf(PETSC_COMM_WORLD,
+                     "Error=%E , ||b-Ax||=%E in %D its , "
+                     "Time: %f [assembly: %f (%.0f\%), solve: %f (%.0f\%)]\n",
+                     error,rnorm,its,tt,ta,ta/tt*100,ts,ts/tt*100);CHKERRQ(ierr);
+
+  PetscBool draw = PETSC_FALSE;
+  ierr = PetscOptionsGetBool(0,"-draw",&draw,0);CHKERRQ(ierr);
+  if (draw) {
+    ierr = VecView(x,PETSC_VIEWER_DRAW_WORLD);CHKERRQ(ierr);
+  }
+
+  ierr = KSPDestroy(&ksp);CHKERRQ(ierr);
+  ierr = MatDestroy(&A);CHKERRQ(ierr);
+  ierr = VecDestroy(&x);CHKERRQ(ierr);
+  ierr = VecDestroy(&b);CHKERRQ(ierr);
+  ierr = IGADestroy(&iga);CHKERRQ(ierr);
+
+  ierr = PetscFinalize();CHKERRQ(ierr);
+  return 0;
+}
 Poisson: Poisson.o chkopts
 	${CLINKER} -o $@ $< ${PETIGA_LIB}
 	${RM} -f $<
+LoggChallenge: LoggChallenge.o chkopts
+	${CLINKER} -o $@ $< ${PETIGA_LIB}
+	${RM} -f $<
 Bratu: Bratu.o BratuFJ.o chkopts
 	${CLINKER} -o $@ $< BratuFJ.o ${PETIGA_LIB}
 	${RM} -f $< BratuFJ.o bratufj.mod
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