How to find Matrix Inverse in VB6?

[Ben321]

I was trying to make a matrix inverse function that calculates the inverse of a matrix (when used with a matrix used in transforms, the inverse matrix can be used to the produce inverse transformation). Here's the code I wrote for finding a 3x3 matrix's inverse. But the resulting inverse matrix doesn't correctly produce an inverse transformation when used in a transformation function. Please help.

Private Function Inverse3x3(ByRef Matrix() As Double) As Double()
Dim MIn() As Double
Dim MMinors(2, 2) As Double
Dim MMinCof(2, 2) As Double
Dim MMinCofAdj(2, 2) As Double
Dim MOut(2, 2) As Double
Dim Determ As Double
MIn() = Matrix()

MMinors(0, 0) = MIn(1, 1) * MIn(2, 2) - MIn(2, 1) * MIn(1, 2)
MMinors(1, 0) = MIn(0, 1) * MIn(2, 2) - MIn(2, 1) * MIn(0, 2)
MMinors(2, 0) = MIn(0, 1) * MIn(1, 2) - MIn(1, 1) * MIn(0, 2)
MMinors(0, 1) = MIn(1, 0) * MIn(2, 2) - MIn(2, 0) * MIn(1, 2)
MMinors(1, 1) = MIn(0, 0) * MIn(2, 2) - MIn(2, 0) * MIn(0, 2)
MMinors(2, 1) = MIn(0, 0) * MIn(1, 2) - MIn(1, 1) * MIn(0, 2)
MMinors(0, 2) = MIn(1, 0) * MIn(2, 1) - MIn(2, 0) * MIn(1, 1)
MMinors(1, 2) = MIn(0, 0) * MIn(2, 1) - MIn(2, 0) * MIn(0, 1)
MMinors(2, 2) = MIn(0, 0) * MIn(1, 1) - MIn(1, 0) * MIn(0, 1)

For Y = 0 To 2
For X = 0 To 2
If ((X + Y) And 1) = 0 Then MMinCof(X, Y) = MMinors(X, Y) Else MMinCof(X, Y) = -MMinors(X, Y)
Next X
Next Y

MMinCofAdj(1, 0) = MMinCof(0, 1): MMinCofAdj(0, 1) = MMinCof(1, 0)
MMinCofAdj(2, 0) = MMinCof(0, 2): MMinCofAdj(0, 2) = MMinCof(2, 0)
MMinCofAdj(2, 1) = MMinCof(1, 2): MMinCofAdj(1, 1) = MMinCof(2, 1)

Determ = MIn(0, 0) * MMinors(0, 0) - MIn(1, 0) * MMinors(1, 0) + MIn(2, 0) * MMinors(2, 0)

For Y = 0 To 2
For X = 0 To 2
MOut(X, Y) = MMinCofAdj(X, Y) / Determ
Next X
Next Y
Inverse3x3 = MOut()
End Function

My function is based off of the mathematical description of matrix inverses that I found at http://www.mathsisfun.com/algebra/ma...-adjugate.html
No pseudo code was found on that web page, so I had to write mine from scratch. There may be bugs in it, but I thought I did it right. Can someone here please check over my above posted code to see if you can find what's wrong with it. Thanks in advance.

[Stevevb99]

Ben,
I really don't know what you are doing mathematically, but as I look at the code, this is the section I'd check on:
MMinCofAdj(1, 0) = MMinCof(0, 1): MMinCofAdj(0, 1) = MMinCof(1, 0)
MMinCofAdj(2, 0) = MMinCof(0, 2): MMinCofAdj(0, 2) = MMinCof(2, 0)
MMinCofAdj(2, 1) = MMinCof(1, 2): MMinCofAdj(1, 1) = MMinCof(2, 1)

All of your other references are for matrices from 0 to 2, and the first two lines have a pattern of 1,0 -> 0,1; 0,1 -> 1,0
But the third line has 2,1 -> 1,2; 1,1 -> 2,1
seems like that line to follow the pattern would be 2,1 -> 1,2; 1,2 -> 2,1
but then I would also expect one of the lines to be 0,0 -> 0,0; 0,0 -> 0,0 or something...
like i said, I don't understand the math, I'm just doing the monkey see, monkey do look at your code. If I'm totally off base please just ignore me...
Thanks
Steve
Ben - I just tried to read the article on the matrix and I think my head broke... 40 years ago this probably made sense to me...

[Ben321]

Thanks. I think there must have been a typo there.

Update:
Hmm. Just tried it and it still isn't working. Yet I can't see what I did wrong.

[jggtz]

Maybe the attached project could help
I downloaded several years ago from internet
Inside the code come the credits

[Vikash08]

Guys, I am new to VB6. Basically, I need to find the inverse of a matrix(taking the input from a 2D array), and also performing matrix multiplication. Later, I would again store it in an array and perform further calculations. Can someone help me out to do that.

P.S: The input matrix is taken from an array, not from the user.

I would be glad if someone could help me out with some code snippet.

[Code Doc]

The code to do this, if your started from scratch, would likely be enormous, especially if the dimensions of the original matrix were left as a variable. Consider the Maths forum and look for an existing function. I imagine one was written years ago.

Surprisingly, during my entire career as a programmer, I never was required to write this code.

[Vikash08]

Thanks. Code Doc.

I have one another problem.

"Private Sub cmdCalculate_Click()
Dim xl As New Excel.Application, xlwbook As Excel.Workbook, xlsheet As Excel.Worksheet"

I get an error that says "User-defined type not defined" on the above mentioned line. Basically in my project I need to take in values from an excel file (.xls) into an arrayand after manipulation, copy them back to an excel file.

How could I resolve this error?

[jggtz]

Guys, I am new to VB6. Basically, I need to find the inverse of a matrix(taking the input from a 2D array), and also performing matrix multiplication. Later, I would again store it in an array and perform further calculations. Can someone help me out to do that.

P.S: The input matrix is taken from an array, not from the user.

I would be glad if someone could help me out with some code snippet.

Have You tried the attached project in post #4 ?