can you tell me what this makro does?

Public Sub FillMatrix()

    '---
    'This macro fills the matrix on the "RaceMatrix" sheet.
    'It calculates the ELO change for the row driver for each "match"
    'against a column driver based on their positions and ELO scores.
    '---

    Dim raceMatrixSheet As Worksheet
    Dim lastRow As Long, lastCol As Long
    Dim X_Factor As Double
    Dim resultsArray As Variant
    Dim i As Long, j As Long
    
    '--- Performance optimizations ---
    Application.ScreenUpdating = False
    Application.Calculation = xlCalculationManual

    '--- Set a reference to the "RaceMatrix" sheet ---
    On Error Resume Next
    Set raceMatrixSheet = ThisWorkbook.Sheets("RaceMatrix")
    On Error GoTo 0

    If raceMatrixSheet Is Nothing Then
        MsgBox "The required sheet 'RaceMatrix' was not found. Please run the 'CreateRaceMatrix' macro first.", vbCritical, "Sheet Not Found"
        Exit Sub
    End If
    
    raceMatrixSheet.Activate

    '--- Determine the dimensions of the matrix ---
    lastRow = raceMatrixSheet.Cells(raceMatrixSheet.Rows.Count, "B").End(xlUp).Row
    lastCol = raceMatrixSheet.Cells(2, raceMatrixSheet.Columns.Count).End(xlToLeft).Column
    
    '--- Validate that the matrix has data ---
    If lastRow < 4 Or lastCol < 4 Then
        MsgBox "No data found in the matrix to process. Please ensure the 'RaceMatrix' sheet is set up correctly.", vbExclamation, "No Data"
        Exit Sub
    End If
    
    '--- Calculate the 'X' Factor (highest position number) once ---
    X_Factor = Application.WorksheetFunction.Max(raceMatrixSheet.Range("A4:A" & lastRow))
    
    '--- Resize an array to hold all the results ---
    ReDim resultsArray(1 To lastRow - 3, 1 To lastCol - 3)

    '--- Main loop to calculate ELO change for each cell ---
    ' Loop through each row driver (Player 1)
    For i = 4 To lastRow
        ' Loop through each column driver (Player 2)
        For j = 4 To lastCol
            
            ' --- Get Player 1 (Row) Data ---
            Dim p1_pos As Double
            Dim p1_name As String
            Dim p1_elo As Double
            p1_pos = CDbl(raceMatrixSheet.Cells(i, 1).Value)
            p1_name = raceMatrixSheet.Cells(i, 2).Value
            p1_elo = CDbl(raceMatrixSheet.Cells(i, 3).Value)
            
            ' --- Get Player 2 (Column) Data ---
            Dim p2_pos As Double
            Dim p2_name As String
            Dim p2_elo As Double
            p2_pos = CDbl(raceMatrixSheet.Cells(1, j).Value)
            p2_name = raceMatrixSheet.Cells(2, j).Value
            p2_elo = CDbl(raceMatrixSheet.Cells(3, j).Value)
            
            ' --- Apply Rules to Calculate ELO Change ---
            Dim eloChange As Double
            
            If p1_name = p2_name Then
                ' Rule 1: Driver vs. themselves
                eloChange = 0
            ElseIf p1_pos = p2_pos Then
                ' Rule 2: Drivers have the same position
                eloChange = 0
            Else
                ' Calculate the expected score for Player 1 (Row Player)
                Dim expectedScore As Double
                expectedScore = 1 / (1 + 10 ^ ((p2_elo - p1_elo) / 400))
                
                If p1_pos < p2_pos Then
                    ' Rule 3: Player 1 wins (lower position is better)
                    ' K * (Actual Score - Expected Score) => K * (1 - Expected)
                    eloChange = (100 / X_Factor) * (1 - expectedScore)
                Else ' p1_pos > p2_pos
                    ' Rule 4: Player 1 loses
                    ' K * (Actual Score - Expected Score) => K * (0 - Expected)
                    eloChange = (100 / X_Factor) * (0 - expectedScore)
                End If
            End If
            
            ' --- Store the calculated value in our results array ---
            resultsArray(i - 3, j - 3) = eloChange
            
        Next j
    Next i
    
    '--- Write the entire results array to the sheet in one operation ---
    raceMatrixSheet.Range("D4").Resize(UBound(resultsArray, 1), UBound(resultsArray, 2)).Value = resultsArray
    
    '--- Optional: Add number formatting to the results ---
    raceMatrixSheet.Range("D4").Resize(UBound(resultsArray, 1), UBound(resultsArray, 2)).NumberFormat = "0.00"

    '--- Restore application settings ---
    Application.Calculation = xlCalculationAutomatic
    Application.ScreenUpdating = True

    MsgBox "The ELO Matrix has been filled successfully!", vbInformation, "Success"

End Sub