# Matrix multiply

1. Jul 27, 2008

### yeeyee

Thank you
1. What is the value of the following matrix multiplication

2. $$A^{-1}DA^{T}=?$$
D is diagonal matrix

3. and how to find D to make $$a_i C Z$$

4. $$A^{-1}DA^{T}$$

$$a_i$$ is elements of $$A^{-1}$$

Last edited: Jul 27, 2008
2. Jul 27, 2008

### yeeyee

C is "belongs to" Z, I mean

I can't write a \belongto

3. Jul 27, 2008

### HallsofIvy

Staff Emeritus
You want the components of A-1 integers? I'm not sure what your question is. If the components of A itself are integers and A has determinant = 1, then the components of A-1 are integers. D has nothing to do with that- especially since you haven't told us anything about ADA-1. Is there some condition on that?

Oh, and $a_n \in Z$ is written [ itex ] a_n\in Z[ /itex ], without the spaces, of course.