# Verify matrix is unitary

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1. Dec 22, 2014

### andphy

Hi,

A unitary matrix should have it transpose conjugate equal to its inverse. Please confirm that this statement is correct and check attached matrix as they are not equal and in doubt if I did correctly.

Thanks.

#### Attached Files:

• ###### Unitary Matrix verification.JPG
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2. Dec 22, 2014

### Clear Mind

Hi,
suppose to have an unitary matrix ($U \in \mathbb{C}^{n \times n}$, so that $U^{\dagger}=U^{-1}$), if you want to verify the unitariety of your matrix, just check if $UU^{\dagger}= \mathbb{I}$.

3. Dec 22, 2014

### andphy

That helps thank you.

4. Dec 23, 2014

### Fredrik

Staff Emeritus
Are you saying (in the attached file) that $\begin{pmatrix}i & 0\\ 0 & 1\end{pmatrix}$ is the inverse of $\begin{pmatrix}1 & 0\\ 0 & i\end{pmatrix}$? It's not. To see this, just multiply these two matrices together.

5. Dec 30, 2014

### HallsofIvy

You have at one point, that the "transpose conjugate" of $\begin{bmatrix}1 & 0 \\ 0 & i\end{bmatrix}$ is $\begin{bmatrix}1 & 0 \\ 0 & -i\end{bmatrix}$. That is correct and that is the inverse matrix.

Below that, you have "inverse matrix" and $\begin{bmatrix} i & 0 \\ 0 & 1\end{bmatrix}$. I don't know where that came from!

6. Jan 3, 2015

### andphy

Right the product will result in the inverse:

1 0
0 1

correct ?

Last edited: Jan 3, 2015
7. Jan 3, 2015

### Fredrik

Staff Emeritus
What product? The product of the two matrices in post #5 is $\begin{pmatrix}i & 0 \\ 0 & i\end{pmatrix}$. As HallsofIvy said, the inverse of $\begin{pmatrix}1 & 0\\ 0 & i\end{pmatrix}$ is $\begin{pmatrix}1 & 0\\ 0 & -i\end{pmatrix}$. The product of these two matrices is the identity matrix.

8. Jan 4, 2015

### andphy

sorry meant to say identity matrix (not inverse) - thank you.