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A matrix, by simplest definition, is a grid of numbers . It can have one or more horizontal rows and one or more vertical columns . Figure 18-1 shows some matrices.
Any particular matrix is usually represented by some variable, such as M . To refer to a specific cell in a matrix, you use the variable name with the row and column number in subscript. For example, if the 3—3 matrix in Figure 18-1 is called M , then M2,3 is equal to 6, as it refers to the second row, third column.
The cells of a matrix can contain not only simple numbers, but also formulas and variables . If youve ever used a spreadsheet, that is basically one big matrix. You can have one cell hold the sum of a column, and another cell multiplies that sum by some fraction thats held in another cell, and so forth. So you see that matrices can be pretty useful.
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