# Thread: MMULT Function (2K & XP)

1. ## MMULT Function (2K & XP)

Say Array 1 & Array 2 = 4 cells each containing 4 numbers. Using the MMULT Function what do the values in the cells reflect. I am using Ctrl + Shift + Enter to enter the array, but I can't fathom out the results. <img src=/S/scratch.gif border=0 alt=scratch width=25 height=29>

2. ## Re: MMULT Function (2K & XP)

It depends on how they are arranged and how you enter the formula.

MMULT multiplies Matrices (arrays) together. It is like several sumproducts done on each one. The HELP in XL gives the formula used. Here is an Explanation of Matrix Multiplication -- From MathWorld
If you provided the 2 arrays and the MMULT you used we could describe it with those details.

The final product has the number of rows of the 1st array and the columns of the 2nd array. The columns of the first array must equal the rows of the 2nd array to be able to multiply.

Steve

3. ## Re: MMULT Function (2K & XP)

MMULT performs matrix (array) multiplication.

In the screenshot below, I2:K4 contains the array formula =MMULT(B2:C4,E2:G3)
Let's look at J2.
This is the cell in the first row and second column of I2:K4.
It is calculated by taking the first row of B2:C4 and the second column of E2:G3 and combining them as follows:
Multiply the corresponding elements and add the result.
In other words, multiply B2 with F2, and multiply C2 with F3, then add the products:
1 * 3 + 2 * 6 = 3 + 12 = 15

To be able to perform matrix multiplication, the number of columns in the first argument must be equal to the number of rows in the second argument, because the elements of these will be multiplied. the resulting matrix has as many rows as the first argument, and as many columns as the second argument.

4. ## Re: MMULT Function (2K & XP)

Many Thanks Hans & Steve. You have both made it easier to understand I will try & get my head round it <img src=/S/dizzy.gif border=0 alt=dizzy width=15 height=15>

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