My data is a matrix `X`

with the dimension `100 \times 3`

, whose each element follows a Poisson distribution. Therefore, each element of it must be nonnegative. I wonder how I can declare such matrix in the data block? because an error message reminds me of defining `X`

correctly.

You can define a 2D array of non-negative integers like:

```
int<lower=0> X[100, 3];
```

Does this solve your error? If not what was the message?

Thanks!