# Matrix operation

1. Mar 24, 2007

### johnchau123

In my note, it said that

Counting multiplication and division only, in solving linear equations (matrix operation),

Elimination of first row: total n^2 operations

So, forward elimination operations for the matrix is Σ(2 to n) k^2 = n*(n+1)*(2n+1)/6

I have tried to solve the equations but it seem do not need n^2 steps.

Can anyone tell me conceptually why it needs n^2 operations to eliminate the first row?

Thanks.

2. Mar 24, 2007

### matt grime

You have to eliminate the firsty entry, so you add a multiple of another row - that is n multiplications. Then you need to do the second entry in the row. That is another n multiplications in another row. You do this n times, so that is n*n operations.

3. Mar 24, 2007

### johnchau123

But i have the following interpretation

Eliminate the first entry and this is n multiplication
Then, I do it n-1, including the first time.

So, I think it is n*(n-1).

4. Mar 24, 2007

### matt grime

To be honest, I'd like you to say what it is that you're doing precisely. I'm not aware of anytime I'd actually want to eliminate the entire first row (of what, by the way? nxn matrix? Why?)

5. Mar 24, 2007

### johnchau123

The following link is a picture which shows what my note says.

Last edited by a moderator: Apr 22, 2017
6. Mar 24, 2007