Need Help Deciphering this Code

[lexbung]

Hello,

I just had to learn VBA for my internship this summer due to a project I had to do. The project is basically figuring out how a pre-built model works. Thanks to Google and previous questions/guides in this forum, I've been able to figure out the bulk of the model, except one Sub (below).

I understand the Sub itself will be out of context but I posted it to give context to the lines I don't understand (bolded and italicized).

What does it mean (or in general) when the code is "expression1()=expression1() + expression2"? I'm having trouble wording it for Google or the forum hence why I had to make a thread about it.

Some help would be appreciated.

Please and thanks.

Sub CutEmLoose(Liabs As Range)Dim NumRows As Long, RowNum As Long, ModAmt As Double
Dim LiabAmts() As Double, LGDAmts() As Double, LossRates() As Double
Dim i As Long, ws As Worksheet
    
    Set ws = ActiveWorkbook.Worksheets("Liability Inputs")
    NumRows = Application.Max(Liabs.Columns(1))


ReDim LiabAmts(1 To NumRows)
ReDim LGDAmts(1 To NumRows)
ReDim LossRates(1 To NumRows)
    
    For i = 3 To Liabs.Rows.Count + 2
        RowNum = Liabs.Cells(i - 2, 1).Value
        ModAmt = Liabs.Cells(i - 2, 8).Value
        If Liabs.Cells(i - 2, 11).Value <> "" Then

LiabAmts(RowNum) = LiabAmts(RowNum) + ModAmt
If ModAmt > 0 Then LGDAmts(RowNum) = LGDAmts(RowNum) + (Liabs.Cells(i - 2, 11) * ModAmt)
If ModAmt > 0 Then LossRates(RowNum) = LossRates(RowNum) + (Liabs.Cells(i - 2, 12) * ModAmt)
       
 End If
    Next i
    For i = 3 To NumRows
        If LiabAmts(i) > 0 Then
            ws.Cells(i, 21).Value = LGDAmts(i) / LiabAmts(i)
            ws.Cells(i, 22).Value = LossRates(i) / LiabAmts(i)
        End If
    Next i
End Sub

 

[CalcSux78]

LiabAmts is an array variable. The first bold line is adding ModAmt to the value of the LiabAmts array with the index of RowNum.

Here's a good article on how arrays work: The Complete Guide to Using Arrays in Excel VBA - Excel Macro Mastery