VBA Matrix Operations Help Needed.

[dennygibson]

You Dim-ed Del1St and W1St as Variant, and plain variants don't take an Index (IZ)

I did not see where Z1St was Dim-ed at all

            Del1St(IZ) = Del1  'Type Mismatch
            W1St(IZ) = W1     'Type Mismatch
            Z1St(IZ) = Z1       'Type Mismatch

I'm guessing you wanted

           Dim  Del1St(1 to 20) As Double
           Dim  W11St(1 to 20) As Double
           Dim  Z1St(1 to 20) As Double