// return this + that
public SparseVector plus(SparseVector that) {
if (this.N != that.N) throw new RuntimeException("Vector lengths disagree");
SparseVector c = new SparseVector(N);
for (int i : this.st.keys()) c.put(i, this.get(i)); // c = this
for (int i : that.st.keys()) c.put(i, that.get(i) + c.get(i)); // c = c + that
return c;
}
// return the dot product of this vector with that vector
public double dot(SparseVector that) {
if (this.N != that.N) throw new RuntimeException("Vector lengths disagree");
double sum = 0.0;
// iterate over the vector with the fewest nonzeros
if (this.st.size() <= that.st.size()) {
for (int i : this.st.keys()) if (that.st.contains(i)) sum += this.get(i) * that.get(i);
} else {
for (int i : that.st.keys()) if (this.st.contains(i)) sum += this.get(i) * that.get(i);
}
return sum;
}
// test client
public static void main(String[] args) {
SparseVector a = new SparseVector(10);
SparseVector b = new SparseVector(10);
a.put(3, 0.50);
a.put(9, 0.75);
a.put(6, 0.11);
a.put(6, 0.00);
b.put(3, 0.60);
b.put(4, 0.90);
StdOut.println("a = " + a);
StdOut.println("b = " + b);
StdOut.println("a dot b = " + a.dot(b));
StdOut.println("a + b = " + a.plus(b));
}
// return alpha * this
public SparseVector scale(double alpha) {
SparseVector c = new SparseVector(N);
for (int i : this.st.keys()) c.put(i, alpha * this.get(i));
return c;
}
// return the 2-norm
public double norm() {
SparseVector a = this;
return Math.sqrt(a.dot(a));
}