Dear all,

I am trying to build a function, my attempt is in the code below

```
vector neighbors_stan( int Minc[M, N], int M, int N) {
//int n = dims(Minc)[1]; // Number of nodes
int max_neighbors = (M * (M - 1)) / 2; // Maximum number of possible neighbors
vector[max_neighbors] neighbor_indices;
int index = 1; // Index to keep track of position in the neighbor_indices vector
// Iterate over the upper triangular part of the matrix
for (i in 2:M) {
for (j in 1:(i - 1)) {
if (Minc[i, j] == 1) {
neighbor_indices[index] = j; // Store the neighbor
index += 1;
}
}
}
```

I am getting the following error:

```
3: vector neighbors_stan(int Minc[M,N], int M, int N) {
^
4: int max_neighbors = (M * (M - 1)) / 2; // Maximum number of possible neighbors
5: vector[max_neighbors] neighbors; // Initialize a vector to store neighbors
-------------------------------------------------
"," or ")" expected after function argument declaration.
```

As this function, I have another ones depending on the matrix Minc. I tried to use the `matrix`

type instead of of the `int`

array and it worked, the issue is that at some point, I need to get an index in function of this matrix, to declare another vector, something like this.,

```
int N_edges; // total numbere of edges
int nei[N_edges]; //vector stacking up the direected neighbors of each node
N_edges = sum(adjmatinf,N,N);
```

if I use the `matrix`

type, the result of the sum above for `N_edges`

will be real, that cannot be use as an index. Since Stan does not allow coversion from real to integer, Do you have any suggestion for me to solve this issue?

Thanks in advance,

Alejandro.