Correct the documentation for crs_matrix.h
Thanks to Joydeep Biswas for reporting this.
Change-Id: Iae5fc2274644aab40f2f922a671f65da15ae71fc
diff --git a/include/ceres/crs_matrix.h b/include/ceres/crs_matrix.h
index c9fe8f7..8c470cd 100644
--- a/include/ceres/crs_matrix.h
+++ b/include/ceres/crs_matrix.h
@@ -44,17 +44,35 @@
int num_rows;
int num_cols;
- // A compressed row matrix stores its contents in three arrays.
- // The non-zero pattern of the i^th row is given by
+ // A compressed row matrix stores its contents in three arrays,
+ // rows, cols and values.
//
- // rows[cols[i] ... cols[i + 1]]
+ // rows is a num_rows + 1 sized array that points into the cols and
+ // values array. For each row i:
//
- // and the corresponding values by
+ // cols[rows[i]] ... cols[rows[i + 1] - 1] are the indices of the
+ // non-zero columns of row i.
//
- // values[cols[i] ... cols[i + 1]]
+ // values[rows[i]] .. values[rows[i + 1] - 1] are the values of the
+ // corresponding entries.
//
- // Thus, cols is a vector of size num_cols + 1, and rows and values
- // have as many entries as number of non-zeros in the matrix.
+ // cols and values contain as many entries as there are non-zeros in
+ // the matrix.
+ //
+ // e.g, consider the 3x4 sparse matrix
+ //
+ // [ 0 10 0 4 ]
+ // [ 0 2 -3 2 ]
+ // [ 1 2 0 0 ]
+ //
+ // The three arrays will be:
+ //
+ //
+ // -row0- ---row1--- -row2-
+ // rows = [ 0, 2, 5, 7]
+ // cols = [ 1, 3, 1, 2, 3, 0, 1]
+ // values = [10, 4, 2, -3, 2, 1, 2]
+
vector<int> cols;
vector<int> rows;
vector<double> values;
