Mining and commodities trader Glencore dipped in early deals on Wednesday after the stock went ex-dividend, but losses were quickly erased after a rating upgrade by Investec.The broker said it has lifted the stock from 'hold' to 'add' and raised its target price for from 360p to 380p following last month's interim report from the group, at which it unveiled a share buyback worth $1bn.It believes the company has "substantial scope" to return funds to shareholders in the coming years.After a review of UK-listed miners, Deutsche Bank has said that Vedanta Resources is its top-ranked producer and upgraded its rating for the shares from 'hold' to 'buy'. As for the other miners under its coverage, Rio Tinto and BHP Billtion are second and third on the list respectively and are both ranked as 'buys'.In contrast, precious metal stocks dominate the bottom rankings due to declining commodity prices and high capital expenditure. As part of its review, the bank has downgraded its ratings for Randgold Resources and African Barrick Gold from 'buy' to 'hold'.Just Eat shares surged on Wednesday after Jefferies initiated coverage of the stock with a 'buy' rating.The broker said that the recently-listed online takeaway delivery marketplace "demonstrates the clearest valuation upside in our UK digital peer group".BC