/// <summary>
/// Put the matrix in sorted form
/// </summary>
/// <param name="m"></param>
/// <param name="constructor">The constructor for a null element of T</param>
/// <param name="toIgnore"></param>
/// <returns></returns>
private static Matrix <T> ToSortedForm <T>(
this Matrix <T> m, Func <T> constructor, int toIgnore = 0)
where T : FieldMember, new()
{
Matrix <T> n = m.SortNullRows(constructor, toIgnore);
int rowsSorted = -1;
// Sort all the rows by switching
while (!n.IsSorted(constructor, toIgnore))
{
rowsSorted++;
List <int> rows = Enumerable.Range(rowsSorted,
n.Height - n.AmountOfNullRows(toIgnore) - rowsSorted).ToList();
int min = rows.Select(i => n.GetPivot(i, constructor, toIgnore)).Min();
int next = rows.First(i => n.GetPivot(i, constructor, toIgnore) == min);
if (next == rowsSorted)
{
continue;
}
RowOperation <T> .SwitchingOperation(next, rowsSorted).ActOn(n);
}
return(n);
}
/// <summary>
/// Scale the rows so that each pivot is a 1
/// </summary>
/// <param name="m"></param>
/// <param name="constructor"></param>
/// <param name="toIgnore"></param>
/// <returns></returns>
private static Matrix <T> ToUnitPivots <T>(
this Matrix <T> m, Func <T> constructor, int toIgnore = 0)
where T : FieldMember, new()
{
Matrix <T> n = m.ToEchelonForm(constructor, toIgnore);
int i = 0;
foreach (var vector in n[VectorType.Row])
{
if (n.GetPivot(i, constructor, toIgnore) == -1)
{
continue;
}
try
{
T scale = constructor().Unit <T>()
.Multiply(vector[n.GetPivot(i, constructor, toIgnore)].Inverse <T>());
RowOperation <T> .ScaleOperation(i, scale).ActOn(n);
}
catch (IncompatibleOperationException)
{
throw new ImpossibleEchelonFormException();
}
i++;
}
return(n);
}
public static Matrix <T> ToEchelonForm <T>(
this Matrix <T> m,
Func <T> constructor,
int toIgnore = 0)
where T : FieldMember, new()
{
Matrix <T> n = m.ToSortedForm(constructor);
int from = -1;
// Put the rows in echelon form (some substitution will be required)
while (!n.IsEchelon(constructor, toIgnore))
{
from++;
// Substitution can unsort the rows
if (!n.IsSorted(constructor, toIgnore))
{
n = n.ToSortedForm(constructor, toIgnore);
}
List <int> rows = Enumerable.Range(from + 1,
n.Height - n.AmountOfNullRows(toIgnore) - from - 1).ToList();
int pivot = n.GetPivot(from, constructor, toIgnore);
foreach (var to in rows)
{
if (n.GetPivot(from, constructor, toIgnore) <
n.GetPivot(to, constructor, toIgnore))
{
continue;
}
if (n.GetPivot(from, constructor, toIgnore) ==
n.GetPivot(to, constructor, toIgnore))
{
try
{
T scale = n[to, pivot].Negative <T>().Multiply(n[from, pivot].Inverse <T>());
RowOperation <T> .SubstitutionOperation(from, to, scale).ActOn(n);
}
catch (IncompatibleOperationException)
{
throw new ImpossibleEchelonFormException();
}
}
if (n.GetPivot(from, constructor, toIgnore) >
n.GetPivot(to, constructor, toIgnore) &&
n.GetPivot(to, constructor, toIgnore) != -1)
{
RowOperation <T> .SwitchingOperation(from, to).ActOn(n);
}
}
}
return(n);
}
/// <summary>
/// Put all the null rows on the bottom of the matrix
/// </summary>
/// <param name="m"></param>
/// <param name="constructor"></param>
/// <param name="toIgnore"></param>
/// <returns></returns>
private static Matrix <T> SortNullRows <T>(
this Matrix <T> m, Func <T> constructor, int toIgnore = 0)
where T : FieldMember, new()
{
// First clone the matrix so that the original is not changed
Matrix <T> n = new Matrix <T>(m);
// Put all null rows on the bottom of the matrix
while (!n.AreNullRowsBelow(constructor, toIgnore))
{
List <int> toSwitch = n.MisplacedNullRows(constructor, toIgnore);
int next = toSwitch.First();
// Switch the null row with the last non-null row
RowOperation <T> .SwitchingOperation(next, n.Height + toSwitch.Count -
n.AmountOfNullRows(toIgnore) - 1).ActOn(n);
}
return(n);
}
/// <summary>
/// Convert the Matrix to reduced echelon form
/// </summary>
/// <param name="m"></param>
/// <param name="constructor">The constructor to make a null instance of T</param>
/// <param name="toIgnore">The amount of rows that needn't be considered when converting.</param>
/// <returns></returns>
public static Matrix <T> ToReducedEchelonForm <T>(
this Matrix <T> m,
Func <T> constructor,
int toIgnore = 0)
where T : FieldMember, new()
{
// First convert to normal echelon form
Matrix <T> n = m.ToUnitPivots(constructor, toIgnore);
int from = n.Height - n.AmountOfNullRows(toIgnore);
// Put the rows in echelon form (some substitution will be required)
while (!n.IsReducedEchelon(constructor, toIgnore))
{
from--;
List <int> rows = Enumerable.Range(0, from).ToList();
// Go from the bottom to the top
rows.Reverse();
int pivot = n.GetPivot(from, constructor, toIgnore);
foreach (var to in rows)
{
if (!n[to, pivot].IsNull())
{
try
{
T scale = n[to, pivot].Negative <T>().Multiply(n[from, pivot].Inverse <T>());
RowOperation <T> .SubstitutionOperation(from, to, scale).ActOn(n);
}
catch (IncompatibleOperationException)
{
throw new ImpossibleEchelonFormException();
}
}
}
}
return(n);
}
