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 pressure measurements acquired over time at a wellbore of at least one well of interest, and corresponding flow rates from a plurality of wells including the well of interest; defining a reservoir model corresponding to 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, boundary nodes for each formation region, and initial pressures for each formation region; operating a computer to evaluate pressure interference responses among a plurality of wells in the reservoir by solving a fluid flow problem for a structure corresponding to the identified reservoir attributes, comprising the steps of: defining a system of equations comprised of equations of pressure and normal pressure derivative at each boundary node of each formation region and at each well within each formation region, and of merging conditions at boundary nodes that are in common with at least two adjacent formation regions in the reservoir model; and for each of the plurality of wells, solving the system of equations to determine a pressure response at that well in response to unit flow rate at one of the plurality of wells; operating a computer to superpose the data corresponding to measured flow rates from the plurality of wells to the evaluated pressure interference responses to calculate a simulated downhole pressure at the at least one well of interest over time; for at least one well of interest, comparing the simulated downhole pressure at the well of interest over time with data corresponding to the downhole pressure measurements acquired over time at that well of interest; after the comparing step, receiving inputs from a user modifying the reservoir attributes, the modified attribute corresponding to at least one of a shape of a formation region or a connection between formation regions; and then repeating the operating and comparing steps for the structure corresponding to the modified reservoir attributes.