I have a function in Stan that takes as input an array of integers, Index. The function uses the indices to sum over a vector:

I.e.

```
sum(II[Index[i]:])
```

I input the Index array in the data block

```
int M3;
int Index[M3];
```

and input the array of integers into the function as

```
(...,int Index)
```

I am receiving the following error

```
Too many indexes, expression dimensions=0, indexes found=1
```

Is this because Stan only allows a single integer value to be passed to the function? I need the array to be integers because Index[i] must be an integer to perform the following.

```
sum(II[Index[i]:])
```

So I cannot define Index to be of type â€śvectorâ€ť.

Does anyone know how I can pass an array of integers into a function? Or if the error means something else?