Drupal 7. How to send privatemsg message from php?

Question

Drupal

Maybe someone came across the Private messages module of messages on the portal? Drupal 7. How to send Private messages from php?

https://www.drupal.org/project/privatemsg

Perhaps there is a function function($from_uid,$to_uid,$message);
Or analog.
I found several functions, one creates a thread, the other a message, but I can not use them.

Is there a way to simulate a form submission from the user?