code: public static <T extends SparseDoubleVector> SparseMatrix asSparseMatrix(
              List<T> vectors, int columns) {
          return new SparseListMatrix<T>(vectors, columns);
      }
docs: Returns a {@link SparseMatrix} from a list of {@code
  SparseDoubleVector}s. The resulting matrix will be modifiable.  Any
  modifications will affect the vectors stored in the passed in list.