Calculating value of two-variable function in VBA function - excel

Question

I have a function f(x,y) = e^(x+y) and function in VBA like this:
Function Test(n As Integer, x0 As Double, xk As Double, y0 As Double, yk As Double) As Double()
Dim i As Integer
Dim j As Integer
Dim Tablica() As Double
ReDim Tablica(0 To n, 0 To n)
For i = 0 To n
For j = 0 To n
Tablica(j, i) = Exp(x0 + i * (xk - x0) / n + y0 + j * (yk - y0) / n)
Next j
Next i
Test = Tablica
End Function
Is there any way to rewrite this code to work with any function like f(x,y) = x+y etc.?

Answer 1

I interpret your question as how to make the mathematical function an input parameter to the function test. There is no very good way to do this in VBA, but what you can do is to define the function in the code module and then use Application.Run to invoke the function by name from inside test.
Proof of concept:
Function test(f As String, n As Integer, x0 As Double, xk As Double, y0 As Double, yk As Double) As Double()
Dim i As Long, j As Long
Dim Tablica() As Double
ReDim Tablica(0 To n, 0 To n)
For i = 0 To n
For j = 0 To n
Tablica(j, i) = Application.Run(f, x0 + i * (xk - x0) / n, y0 + j * (yk - y0) / n)
Next j
Next i
test = Tablica
End Function
'used like:
Function g(x As Double, y As Double) As Double
g = x - y
End Function
Sub test2()
Range("A1:D4").Value = test("g", 3, 0, 1, 3, 4)
End Sub
Note that you don't need to name the called function f, so that test can work with multiple functions. Unfortunately, VBA lacks a notion of anonymous functions, so you still need to defined your functions as VBA functions (or write your own parser).