What is the ruling on one who swore an oath of divorce upon his wife that she should do something, but she did not do it and instead assigned someone else to do it, and then he discovered after a week that it had not been done, knowing that he was angry at the time of the oath and had intercourse with his wife based on his assumption that the matter had been carried out?

If, by the act you swore upon, you intended the occurrence of the action regardless of who performs it, then no divorce takes place due to the absence of breach, unless your wife refuses to perform it or its performance becomes impossible. Some scholars hold that it is not permissible to enjoy one's wife before the sworn-upon act is done, as it is an oath of breach. If he cohabits with her before that, he must repent and refrain from doing so until the act is completed. However, if you intended for your wife to perform the action immediately, then a breach has occurred, and divorce is binding upon you according to the majority of scholars, in contrast to Ibn Taymiyyah, who holds that an expiation for an oath is due. Anger does not affect the ruling unless it clouds your intellect. Based on this, and given that the latter possibility is more probable, you have divorced your wife. If it is the first or second divorce, you can revoke it before the 'iddah (waiting period) ends, and cohabiting with her is considered a revocation. One must be cautious about toying with oaths of divorce.