1. A method implemented by a programmed computer system for use in executing an order directed to a security traded in a market, comprising: obtaining, with the computer system, a value x representing a percentage of market volume associated with the security; calculating, with the computer system, a plurality of expected market impacts associated with execution of the order over a plurality of different time periods; calculating, with the computer system, a plurality of expected price risks associated with execution of the order over the plurality of different time periods; calculating, with the computer system, a plurality of expected total costs associated with execution of the order over the plurality of different time periods, wherein the plurality of expected total costs are calculated using the plurality of expected market impacts and the plurality of expected price risks; and trading the security via execution of the order by at least a first component and a second component in tandem over a time period at which the calculated expected total cost is minimized for the value x, wherein the first component adjusts trade parameters to maximize spread capture, and the second component determines pockets of liquidity at optimal price points.