Hi,

I’m having trouble creating a multi-variable 2-level linear model using the map_rect function. I’ve used @bnicenboim’s example code from Multi threading version of a simple linear mixed model: y ~ cond + (cond||subj) (And a big thank you for posting it - it’s been a huge help).

My model has a number of population level effects and a couple of random effects `y ~ age_function + mileage_function + month_of_year + production_year + condition + used_car_cpi_score + (age_function + mileage_function||vehicle_map)`

I’ve managed to get it to work with the additional random effects and a couple of population effects (intercept and single variable) but when I run it with more than one population variable it fails.

The error message I get looks like the below

```
Unrecoverable error evaluating the log probability at the initial value.
Exception: Exception: array[multi,...] index: accessing element out of range. index 531 out of range;expecting index to be between 1 and 530 (in 'multithreading/two_level_model.stan' at line 12)
(in 'multithreading/two_level_model.stan' at line 119)
```

Line 12 is part of the function block

```
vector mt(vector phi , vector theta , real[] Y_X_r , int[] n_i ) {
//data
int N = n_i[1]; // number of items in each group (vehicle map)
int K = n_i[2]; // number of columns in the X matrix variables
int Kc = K - 1; //re-creates Kc within the function
int M_1 = rows(theta); // number of random effects/group level effects (r.e.)
vector[N] Y = to_vector(Y_X_r[1:N]); //dependent variable ***LINE 12***
matrix[N, Kc] Xc = to_matrix(Y_X_r[N + 1:N + N * Kc], N, Kc); // extract population level data and convert to a matrix
vector[N] Z_1_1 = to_vector(Y_X_r[N + N * Kc + 1: 2 * N + N * Kc]); //Predictor 1 for the r.e. model matrix (all 1s here)
vector[N] Z_1_2 = to_vector(Y_X_r[2 * N + N * Kc + 1: 3 * N + N * Kc]); //Predictor 2 for the r.e. model matrix
vector[N] Z_1_3 = to_vector(Y_X_r[3 * N + N * Kc + 1: 4 * N + N * Kc]); //Predictor 3 for the r.e. model matrix
```

And line 119 refers to the map_rect function in the model block

```
// likelihood including all constants
//using function "mt" with transformed parameter phi, parameter theta, data per shard, no of obs and pars per shard
target += sum(map_rect(mt, phi, theta, Y_X_r, n_i));
```

The vector `V_J_r`

is created in the transformed data block

```
{
int pos = 1;
int end = 0;
for (n in 1:N_1) { //for each group
n_i[n] = {JN[n], K}; //use shard size anf no of variables for each group
end = pos + n_i[n,1] - 1; // what position to stop
//append row can only be done in pairs so will need to nest them
Y_X_r[n] = to_array_1d( // convert to a row_major format
append_row(append_row(Y[pos:end], to_vector(Xc[pos:end, Kc])), //creates an array with the Y and Xc data for the shard
append_row(Z_1_1[pos:end], append_row(Z_1_2[pos:end], Z_1_3[pos:end]))) // adds the data within each group
);
pos += n_i[n,1];
}
}
```

It looks like the array I’m creating is too big for whatever I’ve indexed but for the life of me I can’t figure out what to change. I’ve been going a round in circles for the last couple of days.

Can anyone see where I’ve gone wrong? The full code and data are attached.

2_level_multi_variable.R (831.6 KB)

2_level_model.stan (5.1 KB)

Thanks,

Michael