import tensorflow as tf


    widths, x_centers = tf.meshgrid(widths, x_centers)
    heights, y_centers = tf.meshgrid(heights, y_centers)

    anchor_centers = tf.stack([x_centers, y_centers], axis=2)
    anchor_centers = tf.reshape(anchor_centers, [-1, 2])

    anchor_sizes = tf.stack([widths, heights], axis=2)
