1. A method of computerized simulation of a giant subsurface reservoir in a data processing system of a plurality of data processors, the computerized simulation being an iterative linear solution of equations for reservoir parameters of a giant subsurface reservoir, the giant subsurface reservoir being simulated as a model partitioned into a number of cells arranged in an organized system of cells, the simulation further being based on geological and fluid characterization information for the cells of the reservoir, the method comprising the computer processing steps of: (a) mapping information from the organized system of cells of the reservoir from an original fine grid scale into a coarse cell grid of a reduced number from the original grid; (b) initializing a postulated system solution matrix in the computer system for reservoir parameters for the coarse cell grid; (c) performing a preconditioned conjugate-gradient extrapolation in the computer system on the initialized postulated system solution matrix received for reservoir parameters for the coarse cell grid; (d) transforming in the computer system the results of the preconditioned conjugate-gradient extrapolation for the coarse cell grid to the original cell grid; and (e) performing an iterative linear solution in the computer system for reservoir parameters for the original grid of cells.