WP get_author_posts_url

function get_author_posts_url($author_id, $author_nicename = '') {
    global $wp_rewrite;
    $auth_ID = (int) $author_id;
    $link = $wp_rewrite->get_author_permastruct();

    if ( empty($link) ) {
        $file = home_url( '/' );
        $link = $file . '?author=' . $auth_ID;
    } else {
        if ( '' == $author_nicename ) {
            $user = get_userdata($author_id);
            if ( !empty($user->user_nicename) )
                $author_nicename = $user->user_nicename;
        }
        $link = str_replace('%author%', $author_nicename, $link);
        $link = home_url( user_trailingslashit( $link ) );
    }

    $link = apply_filters('author_link', $link, $author_id, $author_nicename);

    return $link;
}