Why IoUs not summed?

[onurtore]

Hi!,
In validate function inside the utils/function.py, the code calculates and logs IoU:

    for i in range(nums):
        pos = confusion_matrix[..., i].sum(1)
        res = confusion_matrix[..., i].sum(0)
        tp = np.diag(confusion_matrix[..., i])
        IoU_array = (tp / np.maximum(1.0, pos + res - tp))
        mean_IoU = IoU_array.mean()
        
        logging.info('{} {} {}'.format(i, IoU_array, mean_IoU))

    writer = writer_dict['writer']
    global_steps = writer_dict['valid_global_steps']
    writer.add_scalar('valid_loss', ave_loss.average(), global_steps)
    writer.add_scalar('valid_mIoU', mean_IoU, global_steps)
    writer_dict['valid_global_steps'] = global_steps + 1
    return ave_loss.average(), mean_IoU, IoU_array

The part that I dont understand is, I think the nums variable holds the number of GPUs and code only reports the output of the second GPU. If that is the case, why? Shouldn't be average of two?