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Tutorial: A Module for Linear Regression |
Because IML is built around traditional matrix algebra notation, it is often possible to directly translate mathematical methods from matrix algebraic expressions into executable IML statements. For example, consider the problem of solving three simultaneous equations:
> proc iml; IML ReadyEnter
> reset print;The PRINT option of the RESET command causes automatic printing of results. Notice that as you submit each statement, it is executed and the results are displayed. While you are learning IML or developing modules, it is a good idea to have all results printed automatically. Once you are familiar with SAS/IML software, you will not need to use automatic printing.
Next, set up the matrices A and c. Both of these matrices are input as matrix literals; that is, input the row and column values as discussed in Chapter 2, "Understanding the Language."
> a={3 -1 2, > 2 -2 3, > 4 1 -4}; A 3 rows 3 cols (numeric) 3 -1 2 2 -2 3 4 1 -4 > c={8, 2, 9}; C 3 rows 1 col (numeric) 8 2 9Now write the solution equation, x = A^{-1}c, as an IML statement. The appropriate statement is an assignment statement that uses a built-in function and an operator (INV is a built-in function that takes the inverse of a square matrix, and * is the operator for matrix multiplication).
> x=inv(a)*c; X 3 rows 1 col (numeric) 3 5 2
After IML executes the statement, the first row of matrix X contains the x_{1} value for which you are solving, the second row contains the x_{2} value, and the third row contains the x_{3} value.
Now end the session by entering the QUIT command.
> quit; Exiting IML
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