/// <summary>
/// Evaluates dot operation of vector/matrix lazily.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="x"> [<c>x.Rank == 1 || x.Rank == 2</c>] </param>
/// <param name="y"> [<c>y.Rank == 1 || y.Rank == 2</c>] </param>
/// <returns>
/// <para> The result of dot operation of <paramref name="x"/> and <paramref name="y"/>. </para>
/// <para> - If <c>x.Shape == {p} && y.Rank == {p}</c>, then <c>$ReturnValue.Shape == {1}</c>. </para>
/// <para> - If <c>x.Shape == {p} && y.Shape == {p, n}</c>, then <c>$ReturnValue.Shape == {n}</c>. </para>
/// <para> - If <c>x.Shape == {m, p} && y.Shape == {p}</c>, then <c>$ReturnValue.Shape == {m}</c>. </para>
/// <para> - If <c>x.Shape == {m, p} && y.Shape == {p, n}</c>, then <c>$ReturnValue.Shape == {m, n}</c>. </para>
/// <para> - If the shape patterns does not match with above patterns, throw <see cref="ShapeMismatchException"/>. </para>
/// </returns>
/// <exception cref="ShapeMismatchException"></exception>
public static NdArray <T> Dot <T>(this NdArray <T> x, NdArray <T> y)
{
var xEntity = x.GetOrCopyBuffer();
switch (y.Rank)
{
case 1:
var yEntity = y.GetOrCopyBuffer();
switch (x.Rank)
{
case 1:
return(Dot1x1(xEntity, yEntity));
case 2:
return(Dot2x1(xEntity, yEntity));
default:
break;
}
break;
case 2:
var yTEntity = y.Transpose().ToMutable().GetOrCopyBuffer();
switch (x.Rank)
{
case 1:
return(Dot1x2(xEntity, yTEntity));
case 2:
return(Dot2x2(xEntity, yTEntity));
default:
break;
}
break;
default:
break;
}
Guard.ThrowShapeMismatch($"The ranks of x and y must be 1 or 2. (x.Rank={x.Rank}, y.Rank={y.Rank})");
throw new NotSupportedException();
}