/// <summary>
/// Returns the inner product of this vector with the specified vector.
/// </summary>
/// <param name="that">that the other vector</param>
/// <returns>the dot product between this vector and that vector</returns>
/// <exception cref="ArgumentException">if the lengths of the two vectors are not equal</exception>
public double Dot(SparseVector that)
{
if (_dims != that._dims) throw new ArgumentException("Vector lengths disagree");
var sum = 0.0;
// iterate over the vector with the fewest nonzeros
if (_st.Size() <= that._st.Size())
{
foreach (int i in _st.Keys())
if (that._st.Contains(i)) sum += Get(i) * that.Get(i);
}
else
{
foreach (int i in that._st.Keys())
if (_st.Contains(i)) sum += Get(i) * that.Get(i);
}
return sum;
}
public void Run()
{
var a = new SparseVector(10);
var 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);
Console.WriteLine("a = " + a);
Console.WriteLine("b = " + b);
Console.WriteLine("a dot b = " + a.Dot(b));
Console.WriteLine("a + b = " + a.Plus(b));
Console.ReadLine();
}
/// <summary>
/// Returns the scalar-vector product of this vector with the specified scalar.
/// </summary>
/// <param name="alpha">alpha the scalar</param>
/// <returns>the scalar-vector product of this vector with the specified scalar</returns>
public SparseVector Scale(double alpha)
{
SparseVector c = new SparseVector(_dims);
foreach (int i in _st.Keys()) c.Put(i, alpha * Get(i));
return c;
}
/// <summary>
/// Returns the sum of this vector and the specified vector.
/// </summary>
/// <param name="that">that the vector to add to this vector</param>
/// <returns>the sum of this vector and that vector</returns>
/// <exception cref="ArgumentException">if the dimensions of the two vectors are not equal</exception>
public SparseVector Plus(SparseVector that)
{
if (_dims != that._dims) throw new ArgumentException("Vector lengths disagree");
var c = new SparseVector(_dims);
foreach (int i in _st.Keys()) c.Put(i, Get(i)); // c = this
foreach (int i in that._st.Keys()) c.Put(i, that.Get(i) + c.Get(i)); // c = c + that
return c;
}
