I have a matrix where the diagonal elements are meaningless. Usually I just fill them with 0, or infinities. The problem is that when I MatrixPlot this matrix, the diagonal elements affect the gradient scale. I just want to exlucde the diagonal from the plot, leave it blank. How can I do this?

**Example:**

```
mat = RandomReal[{100, 102}, {10, 10}];
mat2 = mat - DiagonalMatrix@Diagonal@mat;

```

Here `mat2` is a matrix with zeros on the diagonal. When I plot it with `MatrixPlot`, I subtract the minimum element to display the variability of the matrix:

```
MatrixPlot[mat2 - Min@mat2]

```

![enter image description here](https://i.stack.imgur.com/iMkrE.png)

Obviously the variability of `mat2` is hidden by the zeros on the diagonal. This is clearly visible if we plot the original matrix:

```
MatrixPlot[mat - Min@mat]

```

![enter image description here](https://i.stack.imgur.com/G717N.png)