BitMatrix is an automated market maker – so given two assets, it’ll let you swap one for the other. But you have to have the assets in the first place for this to work – so you need a “USDTrent” token that’s backed by USD in Trent’s bank account, eg. An algorithmic stablecoin lets you establish a USDX token that’s backed by BTC instead; with the obvious caveat that if the real value of BTC plummets the token can’t maintain par value.