PROGRAM 3


;  FILENAME:  PROGRAM3.LSP       AUTHOR:  ANTHONY F. ORTIZ

;  THIS PROGRAM COMPUTES THE REAL AND IMAGINARY PARTS OF THE ROOTS OF THE 
;  EQUATION (AX^2 + BX + C) (XLISP PROGRAM).

;  THIS FUNCTION CALLS TWO OTHER FUNCTIONS (READ-COEFFICIENTS AND 
;  COMPUTE-DISPLAY-ROOTS).
(DEFUN SOLVE ()
    (READ-COEFFICIENTS)
    (COMPUTE-DISPLAY-ROOTS A B C))

;  THIS FUNCTION READS THE THREE COEFFICIENTS OF THE EQUATION (AX^2 + BX + C). 
(DEFUN READ-COEFFICIENTS ()
    (PRINC "ENTER COEFFICIENTS FOR THE EQUATION AX^2 + BX + C. ")
    (SETQ A (READ))
    (SETQ B (READ))
    (SETQ C (READ)))

;  THIS FUNCTION COMPUTES AND DISPLAYS THE REAL AND IMAGINARY PARTS OF THE
;  ROOTS OF THE EQUATION (AX^2 + BX + C).
(DEFUN COMPUTE-DISPLAY-ROOTS (A B C)
    (LET (R1 R2 (DISC (- (* B B) (* 4 A C))))
        (COND ((> DISC 0)
            (SETQ R1 (/ (+ (- B) (SQRT DISC)) (* 2 A)))
            (SETQ R2 (/ (+ (- B) (- (SQRT DISC))) (* 2 A)))
            (SETQ I1 0)
            (SETQ I2 0))
        ((= DISC 0)
            (SETQ R1 (/ (- B) (* 2 A)))
            (SETQ R2 (/ (- B) (* 2 A)))
            (SETQ I1 0)
            (SETQ I2 0))
        ((< DISC 0)       
            (SETQ R1 (/ (- B) (* 2 A)))
            (SETQ R2 (/ (- B) (* 2 A)))
            (SETQ I1 (/ (SQRT (ABS DISC)) (* 2 A)))
            (SETQ I2 (- (/ (SQRT (ABS DISC)) (* 2 A))))))
    (TERPRI)
    (PRINC "THE REAL AND IMAGINARY PARTS OF EACH ROOT ARE ")
    (TERPRI)
    (TERPRI)                                    
    (LIST (LIST R1 I1) (LIST R2 I2))))          

;  OUTFILE:  PROG3.OUT

XLISP version 2.0, Copyright (c) 1988, by David Betz
; loading "init.lsp"
> (load "program3.lsp")
; loading "program3.lsp"
T
> (solve)
ENTER COEFFICIENTS FOR THE EQUATION AX^2 + BX + C. 1.0 2.0 3.0

THE REAL AND IMAGINARY PARTS OF EACH ROOT ARE

((-1 1.414214) (-1 -1.414214))
>




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