/// <summary>
/// Subtracts two tridiagonal matrices.
/// </summary>
/// <param name="T1">The first matrix M<sub>1</sub>.</param>
/// <param name="T2">The first matrix M<sub>2</sub>.</param>
/// <returns>The difference M<sub>1</sub> - M<sub>2</sub>.</returns>
public static TridiagonalMatrix operator -(TridiagonalMatrix T1, TridiagonalMatrix T2)
{
if (T1 == null)
{
throw new ArgumentNullException("T1");
}
if (T2 == null)
{
throw new ArgumentNullException("T1");
}
int n = T1.Dimension;
if (T2.Dimension != n)
{
throw new DimensionMismatchException();
}
TridiagonalMatrix T = new TridiagonalMatrix(n);
// add the elements
// this is a glorified for-next loop structured so as to minimize the
// integer arithmetic required to keep track of two numbers one unit apart
// and avoid if-tests inside the loop
T.SetDiagonalElement(0, T1.GetDiagonalElement(0) - T2.GetDiagonalElement(0));
int i0 = 0;
int i1 = 1;
while (i1 < n)
{
T.SetDiagonalElement(i1, T1.GetDiagonalElement(i1) - T2.GetDiagonalElement(i1));
T.SetSubdiagonalElement(i0, T1.GetSubdiagonalElement(i0) - T2.GetSubdiagonalElement(i0));
T.SetSuperdiagonalElement(i0, T1.GetSuperdiagonalElement(i0) - T2.GetSuperdiagonalElement(i0));
i0 = i1;
i1++;
}
return(T);
}
