1. Apparatus for optically processing for N.times.N matrices A, B, C, and D to calculate the expression CA.sup.-1 B+D, comprising: first modulator means for spatially modulating an optical beam in response to a signal representing a first number, and having a first set of modulation areas arranged as 2N-1 rows; second modulator means for spatially modulating the optical beam exiting the first modulator means in response to signals representing elements in a second row of 2N-1 numbers, and having a second set of modulation areas arranged as 2N-1 columns; third modulator means for spatially modulating the optical beam exiting the second modulator means in response to signals representing elements in a third column of 2N-1 numbers, and having a third set of modulation areas arranged as 2N-1 rows; light detector means having (2N-1).sup.2 light detection areas arranged as a matrix array of 2N-1 rows and 2N-1 columns, where the detection areas provide an array of detector signals in response to light modulated by respective modulation areas of the first, second and third modulator means, each element in the array of detector signals being proportional, respectively, to the product of the first number, a respective element in the second row of numbers, and a respective element in the third column of numbers; accumulator means for storing, adding and shifting the array of detector signals, and having (2N).sup.2 locations arranged as an accumulator matrix array of 2N rows and 2N columns; means for storing the elements of the matrix A in the upper left quadrant of the accumulator array, for storing the elements of the matrix B in the upper right quadrant of the accumulator array, for storing the elements of the matrix D in the lower right quadrant of the accumulator array, and for storing the polarity inverted elements of the matrix C in the lower left quadrant of the accumulator array; and controls means for: (a) providing the negative reciprocal of the upper left-most location of the accumulator array as the first number to the first modulator means; (b) providing the 2N-1 right-most elements of the top row of the accumulator array as the second row of numbers to the second modulator means; (c) providing the 2N-1 bottom-most elements of the left column of the accumulator array as the third column of numbers to the third modulator means; (d) adding the elements of the array of detector signals to corresponding elements in the portion of the accumulator array comprising the 2N-1 right-most columns and the 2N-1 bottom-most rows; (e) shifting the contents of the accumulator array one column to the left and one row to the top; and (f) repeating the operations in (a) through (e) N-1 times, whereby the expression CA.sup.-1 B+D is provided in the upper left quadrant of the accumulator array.