From dfc6dc975e2130af1cbade2d21320a2805b137d6 Mon Sep 17 00:00:00 2001
From: Gard Spreemann <gard.spreemann@epfl.ch>
Date: Tue, 26 Sep 2017 16:35:20 +0200
Subject: Basic functionality working.

---
 src/main.cpp | 115 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)

diff --git a/src/main.cpp b/src/main.cpp
index a6802d8..822aa47 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,6 +1,121 @@
 #include <iostream>
+#include <cmath>
+#include <cassert>
+#include <fstream>
+#include <slepceps.h>
+#include <petscmat.h>
 
 int main(int argc, char ** argv)
 {
+  SlepcInitialize(&argc, &argv, NULL, NULL);
+
+  std::string infile(argv[1]);
+  std::string outfile(argv[2]);
+
+  PetscMPIInt mpi_rank;
+  PetscMPIInt mpi_size;
+  MPI_Comm_rank(PETSC_COMM_WORLD, &mpi_rank);
+  MPI_Comm_size(PETSC_COMM_WORLD, &mpi_size);
+  
+  PetscErrorCode err;
+  Mat L;
+  err = MatCreate(PETSC_COMM_WORLD, &L); CHKERRQ(err);
+  err = MatSetFromOptions(L); CHKERRQ(err);
+
+  PetscViewer viewer;
+  err = PetscViewerBinaryOpen(PETSC_COMM_WORLD, infile.c_str(), FILE_MODE_READ, &viewer); CHKERRQ(err);
+  err = MatLoad(L, viewer); CHKERRQ(err);
+  err = MatAssemblyBegin(L, MAT_FINAL_ASSEMBLY); CHKERRQ(err);
+  err = MatAssemblyEnd(L, MAT_FINAL_ASSEMBLY); CHKERRQ(err);
+
+  PetscInt m;
+  PetscInt n;
+  err = MatGetSize(L, &m, &n); CHKERRQ(err);
+  assert(m == n);
+  PetscPrintf(PETSC_COMM_WORLD, "Laplacian is size %d.\n", m);
+  
+  EPS eps;
+  err = EPSCreate(PETSC_COMM_WORLD, &eps); CHKERRQ(err);
+  err = EPSSetOperators(eps, L, NULL); CHKERRQ(err);
+  err = EPSSetProblemType(eps, EPS_HEP); CHKERRQ(err);
+  err = EPSSetWhichEigenpairs(eps, EPS_SMALLEST_MAGNITUDE); CHKERRQ(err);
+  err = EPSSetFromOptions(eps); CHKERRQ(err);
+
+  PetscPrintf(PETSC_COMM_WORLD, "Solving...\n");
+  err = EPSSolve(eps); CHKERRQ(err);
+
+  PetscInt num_its;
+  err = EPSGetIterationNumber(eps, &num_its); CHKERRQ(err);
+  PetscPrintf(PETSC_COMM_WORLD, "Took %d iterations.\n", num_its);
+  
+  
+  PetscInt num_ev;
+  err = EPSGetConverged(eps, &num_ev); CHKERRQ(err);
+  PetscPrintf(PETSC_COMM_WORLD, "Have %d eigenpairs.\n", num_ev);
+
+  Vec vec;
+  err = MatCreateVecs(L, &vec, NULL); CHKERRQ(err);
+  PetscReal val;
+  PetscReal cutoff = 1e-6;
+  PetscInt estimated_betti = 0;
+  PetscInt vec_size;
+  err = VecGetSize(vec, &vec_size); CHKERRQ(err);
+  
+  Vec vec_r0;
+  if (mpi_rank == 0)
+  {
+    err = VecCreateSeq(PETSC_COMM_SELF, vec_size, &vec_r0); CHKERRQ(err);
+  }
+
+  VecScatter scatter;
+  err = VecScatterCreateToZero(vec, &scatter, &vec_r0); CHKERRQ(err);
+
+  std::ofstream ofs;
+  if (mpi_rank == 0)
+  {
+    ofs.open(outfile, std::ios::out);
+  }
+    
+  for (PetscInt i = 0; i < num_ev; i++)
+  {
+    err = EPSGetEigenpair(eps, i, &val, NULL, vec, NULL); CHKERRQ(err);
+    PetscPrintf(PETSC_COMM_WORLD, "%d: %f\n", i, val);
+
+    if (std::abs(val) < cutoff)
+    {
+      estimated_betti++;
+
+      err = VecScatterBegin(scatter, vec, vec_r0, INSERT_VALUES, SCATTER_FORWARD); CHKERRQ(err);
+      err = VecScatterEnd(scatter, vec, vec_r0, INSERT_VALUES, SCATTER_FORWARD); CHKERRQ(err);
+
+      if (mpi_rank == 0)
+      {
+        PetscReal * tmp;
+        err = VecGetArray(vec_r0, &tmp); CHKERRQ(err);
+        for (PetscInt j = 0; j < vec_size; j++)
+        {
+          ofs << tmp[j] << " ";
+        }
+        ofs << std::endl;
+        err = VecRestoreArray(vec_r0, &tmp); CHKERRQ(err); 
+      }
+    }
+  }
+ 
+
+  PetscPrintf(PETSC_COMM_WORLD, "Estimated Betti number: %d.\n", estimated_betti);
+
+  if (mpi_rank == 0)
+  {
+    ofs.close();
+  }
+
+  err = VecScatterDestroy(&scatter); CHKERRQ(err);
+  err = VecDestroy(&vec); CHKERRQ(err);
+  err = VecDestroy(&vec_r0); CHKERRQ(err);
+  
+  err = EPSDestroy(&eps); CHKERRQ(err);
+  err = MatDestroy(&L); CHKERRQ(err);
+  SlepcFinalize();
   return 0;
 }
-- 
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