VBA Matrix Operations - Why isn't this simple code working?

[Swansonator]

All I am trying to do is multiply two matrices together in vba. This code works if both 'a' and 'b' are square matrices, but this just returns an error, and 'c' has 'error 2015' when I'm trying to de-bug. Any help?

Sub arraytest()

Dim a(1 To 2, 1 To 2) As Variant
Dim b(1 To 2, 1) As Variant
Dim c As Variant


a(1, 1) = 1
a(1, 2) = 2
a(2, 1) = 3
a(2, 2) = 4


b(1, 1) = 5
b(1, 2) = 6


c = Application.MMult(a, b)


For i = 1 To 2
Cells(i, 1) = c(i, 1)
Next i


End Sub

On a related note, how can I assign hard coded values to a 2-d array? Such as

a = array(1, 2 ; 3,4)

 

[pgc01]

Sub arraytest()

Dim b(1 To 2,[B][COLOR=#FF0000] 1[/COLOR][/B]) As Variant

...

b(1, 1) = 5
b(1, [B][COLOR=#FF0000]2[/COLOR][/B]) = 6

...

End Sub

Hi

You are referring to the column 2 in the matrix b, but this matrix does not have a column 2.

Can it be that you meant:

Dim b(1 To 2,[B][COLOR=#FF0000] 1 to 2[/COLOR][/B]) As Variant

?

 

[Swansonator]

I'm so sorry, that was from me changing things around to figure out the problem, I forgot to put them back. Even with that error fixed, it's still not working.

Sub arraytest()

Dim a(1 To 2, 1 To 2) As Variant
Dim b(1 To 2, 1) As Variant
Dim c As Variant


a(1, 1) = 1
a(1, 2) = 2
a(2, 1) = 3
a(2, 2) = 4


b(1, 1) = 5
b(2, 1) = 6


c = Application.MMult(a, b)


For i = 1 To 2
Cells(i, 1) = c(i, 1)
Next i


End Sub

 

[pgc01]

Hi

I guess then that you want the second dimension to be 1?

Use:

Dim b(1 To 2, [B][COLOR=#FF0000]1 to 1[/COLOR][/B]) As Variant

Remarks:
1-

Dim b(1 To 2,[COLOR=#FF0000][B] 1[/B][/COLOR]) As Variant

is, by default

Dim b(1 To 2, [COLOR=#FF0000][B]0 to 1[/B][/COLOR]) As Variant

2 -
You forgot to declare the variable i

3 - Matrix operations use numbers. I usually declare the matirix elements as Double.

 

[Swansonator]

Thank you! I had to keep c as a variant. It wouldn't work as a double, or if I gave it dimensions like this.

dim c(1 to 2, 1 to 1) as double

It worked just fine as follows:

Sub arraytest()

Dim a(1 To 2, 1 To 2) As Double
Dim b(1 To 2, 1 To 1) As Double
Dim c As Variant


a(1, 1) = 1
a(1, 2) = 2
a(2, 1) = 3
a(2, 2) = 4


b(1, 1) = 5
b(2, 1) = 6


c = Application.MMult(a, b)


For i = 1 To 2
Cells(i, 1) = c(i, 1)
Next i


End Sub

 

[pgc01]

I'm glad it helped. You are right, the result is a Variant.

 

[Swansonator]

Thanks, I was trying to solve this issue to work out a Newton-Raphson iteration macro of mine. I got everything working right, but when I multply two matrices in VBA the result is 0 ; 0, when it should be -0.1 ; -0.2. I msgbox the resulting matrix just to make sure Jinv and R are coming out like I think they would, but the multiplication of the two gives zeros.

Sub NewtonRaphson()
'f_1(x1,x2) = x_1^2 + x_2^2 - 4
'f_2(x1,x2) = x_1^2 + x_2 + 1
'J_1(x1,x2) = 2*x_1 + 2*x_2
'J_2(x1,x2) = 2*x_1 - 1


'definitions
Dim x(1 To 2, 1 To 1) As Double
Dim J(1 To 2, 1 To 2) As Double
Dim R(1 To 2, 1) As Double
Dim dx As Variant






'Initial Guess


x(1, 1) = 1
x(2, 1) = 2
R(1, 1) = 1
R(2, 1) = 1


Do Until Abs(R(1, 1)) < 0.0000000001 And Abs(R(2, 1)) < 0.0000000001


J(1, 1) = 2 * x(1, 1)
J(1, 2) = 2 * x(2, 1)
J(2, 1) = 2 * x(1, 1)
J(2, 2) = -1
R(1, 1) = -(x(1, 1) ^ 2 + x(2, 1) ^ 2 - 4)
R(2, 1) = -(x(1, 1) ^ 2 - x(2, 1) + 1)
Jinv = Application.MInverse(J)


strng = ""
For a = 1 To 2
strng = strng & Jinv(a, 1) & "  " & Jinv(a, 2) & "     " & R(a, 1) & vbNewLine
Next a
MsgBox (strng)


[COLOR=#ff0000]dx = Application.MMult(Jinv, R)[/COLOR]


strng = dx(1, 1) & vbNewLine & dx(2, 1)
MsgBox (strng)


For a = 1 To 2
x(a, 1) = x(a, 1) + dx(a, 1)
Next a


Loop


MsgBox (x(1, 1) & vbNewLine & x(2, 1))




End Sub

 

[pgc01]

Hi

I couldn't test it yet, but I see again the same declaration error that you had before:

Dim R(1 To 2, [B][COLOR=#ff0000]1[/COLOR][/B]) As Double

It should be:

Dim R(1 To 2,[B] [COLOR=#ff0000]1 to 1[/COLOR][/B]) As Double

If that's not the whole problem it's at least a part of the problem.

Can you test it?

If it doesn't work I can test it later.

 

[Swansonator]

Perfect! Thank you so much for your help and time.

 

[pgc01]

You're welcome. Thanks for the feedback.