Code to Calculate the product of two matrices won't calculate

Hello,

Yes, I'm a student with an assignment.
But, I fell like I'm most of the way to my solution, although my code isn't working.
I have written the code below to calculate the product of two matrices but I keep getting #NAME? instead of a matrix.

I'm running in Excel - Microsoft Visual Basic 14.5.5 for Mac

Any help would be much appreciated!
Thanks

Please Login or Register  to view this content.

Code Tags Added
Your post does not comply with Rule 3 of our Forum RULES. Use code tags around code.

Posting code between [CODE]Please [url=https://www.excelforum.com/login.php]Login or Register [/url] to view this content.[/CODE] tags makes your code much easier to read and copy for testing, it also maintains VBA formatting.

Highlight your code and click the # icon at the top of your post window. More information about these and other tags can be found at http://www.excelforum.com/forum-rule...rum-rules.html



(Because you are new to the forum, I have added them for you today. Please take a few minutes to read all Forum Rules and comply in the future.)

You don't get any compile errors? I immediately got two compile errors. One for "duplicate declaration" for the Dim A... statement (A is passed to the function in the argument list, too). Another compile error was for the Exit For not within For...Next loop for the third Exit For statement, which is outside of the loop. If you are getting any error statements, be sure to mention them as that is an important part of debugging. I am guessing that both of these statements are superfluous and should be deleted.

The other thing I notice is that you are not defining the size of the C() array anywhere. This will cause a runtime error, in the VBA does not know what size this array is. Either include the limits in your Dim C()... statement, or include a ReDim statement that will set the size of this array before it is used.

Help file for the redim statement: https://msdn.microsoft.com/en-us/library/w8k3cys2.aspx

The function will not just calculate and figure out how big to make the C() array. You have to tell it. If you want it to figure out how large based on the size of the output array, then you can use caller.parent (I think that's it) to determine the size of the output array. If you want to figure out how large the array should be from the input arrays, then use what you know of matrix multiplication to determine the size of the array. According to this http://www.mathsisfun.com/algebra/ma...ltiplying.html the output array will have the same number of columns as the first matrix and the same number of rows as the second matrix, so you could put those values into a redim statement. Or, you can dimension the C array to be larger than any array you ever expect to need. However you choose to do it, VBA is not going to magically know how large to make C(). The programmer needs to somehow instruct VBA how large it will be or how to figure out how large it will be.

Functions must be in a general module not a sheet module
C(i, j) has no dimensions, C must be redim'd to have the same number of rows as matrix A and the same number of columns as matrix b:

ReDim C(1 to a.Rows.count, 1 to b.Columns.Count)

You have an Exit For after the Next k statement but since it is inside the j loop it causes an exit from the J loop after the first iteration, i.e., k loops 1 to 3 but you exit j before the next j statement The statement after the next j is another exit, this time within the i loop so that it causes exit from the i loop. finally, after the next i you have another exit for, but this one is outside of all the loops and refers to nothing.

You never use "exit for" to exit a loop unless you are testing a condition within the loop and you want to exit if the condition is satisfied:

For x = 1 to 10
If x = 7 then Exit for
Next x

For x = 1 to 10
do something
next x
Exit For
This is always wrong and the code will crash

User defined functions are meant to return a calculated value to a worksheet cell or to a variable in some other VB module. In order to return the value, you must set the function to the value within your function's code, usually as the last line:

Function TimesTwo(a as range) as Double
TimesTwo=a*2
End Function
or

Function MultMatrix(...etc...) as Variant
{calculations}
Multmatrix = C
End Function