public SparseMatrix makeLaplacian() {
SparseMatrix laplacian = new SparseMatrix(this.rowDim, this.colDim);
for (int r : this.getRows()) {
Counter row = this.getRow(r);
laplacian.set(r, r, row.sum());
for (int c : row.keySet()) {
laplacian.set(r, c, -1 * row.get(c));
}
}
return laplacian;
}