CompressedRowSparseMatrix::AppendRows and DeleteRows bugfix.

CompressedRowSparseMatrix can store the row and column block structure
but the AppendRows and DeleteRows methods did not pay attention to them.
This meant that it was possible to get to a CompressedRowSparseMatrix
whose block structure did not match the contents of the matrix.

This change fixes this problem.

Change-Id: I1b3c807fc03d8c049ee20511e2bc62806d211b81

internal/ceres/compressed_row_sparse_matrix.cc

@@ -31,6 +31,7 @@
 #include "ceres/compressed_row_sparse_matrix.h"
 
 #include <algorithm>
+#include <numeric>
 #include <vector>
 #include "ceres/crs_matrix.h"
 #include "ceres/internal/port.h"
@@ -215,11 +216,28 @@ void CompressedRowSparseMatrix::DeleteRows(int delta_rows) {
 
   num_rows_ -= delta_rows;
   rows_.resize(num_rows_ + 1);
+
+  // Walk the list of row blocks untill we reach the new number of
+  // rows and then drop the rest of the row blocks.
+  int num_row_blocks = 0;
+  int num_rows = 0;
+  while (num_row_blocks < row_blocks_.size() && num_rows < num_rows_) {
+    num_rows += row_blocks_[num_row_blocks];
+    ++num_row_blocks;
+  }
+
+  row_blocks_.resize(num_row_blocks);
 }
 
 void CompressedRowSparseMatrix::AppendRows(const CompressedRowSparseMatrix& m) {
   CHECK_EQ(m.num_cols(), num_cols_);
 
+  CHECK(row_blocks_.size() == 0 || m.row_blocks().size() !=0)
+      << "Cannot append a matrix with row blocks to one without and vice versa."
+      << "This matrix has : " << row_blocks_.size() << " row blocks."
+      << "The matrix being appended has: " << m.row_blocks().size()
+      << " row blocks.";
+
   if (cols_.size() < num_nonzeros() + m.num_nonzeros()) {
     cols_.resize(num_nonzeros() + m.num_nonzeros());
     values_.resize(num_nonzeros() + m.num_nonzeros());
@@ -239,6 +257,7 @@ void CompressedRowSparseMatrix::AppendRows(const CompressedRowSparseMatrix& m) {
   }
 
   num_rows_ += m.num_rows();
+  row_blocks_.insert(row_blocks_.end(), m.row_blocks().begin(), m.row_blocks().end());
 }
 
 void CompressedRowSparseMatrix::ToTextFile(FILE* file) const {