Matrix Multiplication Function

Category:

Office/VBA

Type:

Snippets

Difficulty:

Intermediate

Author:

Anonymous

Version Compatibility: Visual Basic.NET

More information:

Function accepts n arrays (matrices) for multiplication. It cycles through the parameter array multiplying each matrix, checks that the matrices are conformable and then redimensions the product matrix before running through the multiplication routine.

Instructions: Copy the declarations and code below and paste directly into your VB project.

Declarations:
' (None)

Code:

Function M_Mult(ParamArray IPM() As Variant) As Variant
Dim i As Long, j As Long, k As Long, L As Long, temp As Double
Dim M As Variant, Matrix As Variant, hold As Variant

'***********************************************
'* Function multiplies n matrices.             *
'* Matrices must be conformable:               *
'* Matrix M(i) is mxn and matrix M(i+1) is nxm *
'***********************************************

'Cycle through the parameter array multiplying each matrix
    M = IPM(0)
    For L = LBound(IPM) To UBound(IPM) - 1
    
        'Check that matrices are conformable
        If UBound(M, 2) <> UBound(IPM(L + 1), 1) Then Exit Function
        
        'Redimension the product matrix
        ReDim Matrix(1 To UBound(M, 1), 1 To UBound(IPM(L + 1), 2))
        
        'Multiplication routine
        For i = 1 To UBound(M, 1)
            For j = 1 To UBound(IPM(L + 1), 2)
                For k = 1 To UBound(IPM(L + 1), 1)
                    temp = temp + M(i, k) * IPM(L + 1)(k, j)
                Next k
                Matrix(i, j) = temp
                temp = 0
            Next j
        Next i
        
        M = Matrix
    Next L
    M_Mult = Matrix
End Function