Write a VBA function (named “MultMatrix”, of type “Variant”) to calculate the pr

Question

Write a VBA function (named “MultMatrix”, of type “Variant”) to
calculate the product of two arbitrary matrices in an Excel spreadsheet. Your function should
flag incompatible matrices for multiplication with a “Message Box”. For the following 3 x 3
matrices calculate A*B = C, check your results against the MMULT function in Excel.
(3x3)
A =
5 7 2
1 1 -1
8 8 5
B =
8 -2 3
2 2 4
3 4 1
• The two matrices being multiplied are “Range” arguments to the function; you can access
their sizes with the VBA constructs “.Rows.Count” and “.Columns.Count”. The individual
array elements are accessed with the “.Cells(i,j)” construct.
• The matrix C does not necessarily have the same dimensions as A or B. You may want to
declare the size of the C matrix to do the computations. One possibility is to use dynamically
allocated arrays (see section 2.13 of the Law text, pp 39-42).

Explanation / Answer

               Function MatrixProduct(MatrixRange1, MatrixRange2) As Double  

   Dim m As Integer, n As Integer
   Dim i As Integer, j As Integer

                Dim aRows As Integer, aCols As Integer

   Dim bRows As Integer, bCols As Integer

   Dim A() As Variant, B() As Variant, C() As Variant

   aRows = MatrixRange1.Rows.Count

   aCols = MatrixRange1.Columns.Count

   bRows = MatrixRange2.Rows.Count

   bCols = MatrixRange2.Columns.Count

        If aRows > bRows Then

            i = bRows

        Else

            i = aRows

        End If

        If aCols > bCols Then

            j = bCols

        Else

            j = aCols

        End If

   ReDim A(i, j) As Variant, B(i, j) As Variant, C(i, j) As Variant

   For m = 1 To i

        For n = 1 To j

        A(m, n) = MatrixRange1.Cells(m, n)

        B(m, n) = MatrixRange2.Cells(m, n)

        C(m, n) = A(m, n) * B(m, n)

        Next n

   Next m

   MatrixProduct = C(m, n)

   End Function

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