// return the matrix-vector product b = Ax
public SparseVector times(SparseVector x) {
SparseRowMatrix A = this;
if (N != x.size()) throw new RuntimeException("Dimensions disagree");
SparseVector b = new SparseVector(N);
for (int i = 0; i < N; i++) b.put(i, A.rows[i].dot(x));
return b;
}
/** Sets the given row equal the passed vector */
public void setRow(int i, SparseVector x) {
if (x.size() != numColumns)
throw new IllegalArgumentException("New row must be of the same size as existing row");
rowD[i] = x;
}