1. A method of interactively deriving and validating a computerized model of a hydrocarbon reservoir with downhole measurements from one or more wells in the earth, comprising: receiving data corresponding to downhole measurements acquired over time at a wellbore of at least one well of interest, and corresponding to flow rates from a plurality of wells including the well of interest; receiving inputs from a user identifying attributes of a hydrocarbon reservoir, the attributes comprising shapes and properties of formation regions, connections between formation regions, locations of wells into the formation regions, and a plurality of perforations, each perforation corresponding to an intersection of one of the wells and one of the formation regions; operating a computer to evaluate pressure responses between each of a plurality of wells in the reservoir and the at least one well of interest in the reservoir by solving a fluid flow problem for a structure corresponding to the identified reservoir attributes; operating a computer to superpose the data corresponding to measured flow rates from the plurality of wells to the evaluated pressure responses to calculate a simulated downhole pressure at the at least one well of interest over time; comparing the simulated downhole pressure at the well of interest over time with data corresponding to downhole measurements acquired over time at the at least one well of interest; after the comparing step, receiving inputs from a user modifying the reservoir attributes; and then repeating the operating and comparing steps for the structure corresponding to the modified reservoir attributes; wherein the step of operating the computer to evaluate pressure responses comprises: calculating a pressure interference response at each perforation in response to a unit flow rate at each perforation, comprising: defining a plurality of boundary nodes at boundaries of each of the formation regions; for each of the perforations: assigning a unit flow rate to the perforation and zero flow rate to others of the plurality of perforations; and solving a system of equations to evaluate pressure at each of the boundary nodes in response to the unit flow rate at the perforation; and then, for a selected perforation location: selecting an interfering one of the plurality of perforations; retrieving the pressure at each of the boundary nodes from the solving step in response to a unit flow rate at the selected interfering perforation; and evaluating the pressure at the selected perforation location from the retrieved boundary node pressures, to arrive at a pressure interference response at the selected perforation location to unit flow rate from the interfering perforation; and repeating the selecting, retrieving, and evaluating steps for each of the plurality of perforations as the interfering perforation.