Use MATLAB Global Variables in Visual Basic

Class properties allow an object to retain an internal state between method calls.

Global variables are variables that are declared in the MATLAB^® product with the global keyword. MATLAB Compiler SDK™ automatically converts all global variables shared by the MATLAB files that make up a class to properties on that class.

Properties are useful when you have a large array containing values that do not change often, but are operated on frequently. In such cases, setting the array as a property saves the overhead required to pass it to a method every time it is called.

The following example shows how to use a class property in a matrix factorization class. The example develops a class that performs Cholesky, LU, and QR factorizations on the same matrix. It stores the input matrix as a class property so that it is not passed to the factorization routines.

Consider these three MATLAB files.

Cholesky.m

function [L] = Cholesky()
    global A;
    if (isempty(A))
        L = [];
        return;
    end
    L = chol(A);

LUDecomp.m

function [L,U] = LUDecomp()
    global A;
    if (isempty(A))
        L = [];
        U = [];
        return;
    end
    [L,U] = lu(A);

QRDecomp.m

function [Q,R] = QRDecomp()
    global A;
    if (isempty(A))
        Q = [];
        R = [];
        return;
    end
    [Q,R] = qr(A);

These three files share a common global variable A. Each function performs a matrix factorization on A and returns the results.

To build the class:

1. Create a compiler project named mymatrix with a version of 1.0.

2. Add a single class called myfactor to the component.

3. Add the above three MATLAB files to the class.

4. Build the component.

Use the following Visual Basic^® subroutine to test the myfactor class:

Sub TestFactor()
    Dim x(1 To 2, 1 To 2) As Double
    Dim C As Variant, L As Variant, U As Variant, _
    Q As Variant, R As Variant
    Dim factor As myfactor
    
    On Error GoTo Handle_Error
    Set factor = New myfactor
    x(1, 1) = 2#
    x(1, 2) = -1#
    x(2, 1) = -1#
    x(2, 2) = 2#
    factor.A = x
    Call factor.cholesky(1, C)
    Call factor.ludecomp(2, L, U)
    Call factor.qrdecomp(2, Q, R)
    Exit Sub
Handle_Error:
    MsgBox (Err.Description)
End Sub

Run the subroutine, which does the following:

1. Creates an instance of the myfactor class

2. Assigns a double matrix to the property A

3. Calls the three factorization methods