Problem with MDETERM

[ekozyreff]

The function MDETERM is miscalculating in the Excel installed in my computer.

The matrix in A1:G7 has two identical rows, thus its determinant is zero, as shown in cell I2, where I use the function =MDETERM(A1:G7).
The matrix in A9:G15 is the transpose of the first matrix, so its determinant should be zero as well, but Excel miscalculates it in cell I10, where I wrote =MDETERM(A9:G15).


Does anyone know what the problem is?
Thanks!

 

[pgc01]

Hi
Welcome to the board

You did not post any example so this is guess work.

Maybe the value for the determinant is very small and it's just the usual floating point rounding error?

If you post an example it's easy to check.

Anyway, as you may know, excel, like most programs that perform floating point calculations, follows the IEEE 754 standard and so small rounding errors are to be expected.

Can't say more without real data.

 

[ekozyreff]

Hi there!

Thanks for your answer!
I did post an example, using an image.
Regarding rounding errors: MS Excel's help page says that the program can have errors in the magnitude of 10E-16. Also, all entries of the matrix are integers, so the determinant must be integer as well.
Regards,

 

[XOR LX]

Hi.

Not sure if it's just my browser, but I can't seem to see your picture?

Regards

 

[ekozyreff]

My mistake. Here is the image:

Thank you!

 

[XOR LX]

Still can't see anything. Can you confirm that you do?

Regards

 

[ekozyreff]

I see it.
Let me post the picture again from another address. Here it is:

Thanks!

 

[XOR LX]

Unfortunately it looks like PGC's right.

I played about with a few different sets of values and the small difference due to rounding errors crops up quite often using this function.

Regards

 

[pgc01]

Hi

Remark: in this special case, since we are dealing with only integer values, it's really dependent on the algorithm that MS uses.

With the usual algorithms that rely only upon multiplications we can have the exact result, no rounding error, as long as we don't go beyond the maximum value allowed.