Hi everyone,

I am trying to figure out why this code does not work.

Basically I need a vector of real numbers. I read in several posts that vector[N] a; should be preferred to real a[N]; so am I using the first notation.

The problem is that the function gp_exponential_cov returns an error, although it seems it should be working:

```
Ill-typed arguments supplied to function 'gp_exponential_cov'. Available signatures:
(real[], real, real) => matrix
(real[], real[], real, real) => matrix
(vector[], real, real) => matrix
(vector[], real, real[]) => matrix
(vector[], vector[], real, real) => matrix
(vector[], vector[], real, real[]) => matrix
Instead supplied arguments of incompatible type: vector, real, real.
```

What is the difference between `vector`

and `vector[]`

?

Why is the function not working?

When I do real[N] a; no issues.

Thank you,

Marco