PROGRAM VECTOR
C FINDS THE DOT PRODUCT OF TWO 2-D VECTORS

C     ORIGINALLY WRITTEN WHILE A STUDENT AT UW-RF, 1992

C     COPYRIGHT (C) 1992, 2007 JIM HALL, JHALL@FREEDOS.ORG
C Permission is hereby granted, free of charge, to any person obtaining a copy
C of this software and associated documentation files (the "Software"), to deal
C in the Software without restriction, including without limitation the rights
C to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
C copies of the Software, and to permit persons to whom the Software is
C furnished to do so, subject to the following conditions:
C 
C The above copyright notice and this permission notice shall be included in
C all copies or substantial portions of the Software.
C 
C THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
C IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
C FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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C OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
C THE SOFTWARE.


      PRINT *, 'VECTOR - FINDS THE DOT PRODUCT OF TWO VECTORS'

   10 PRINT *, 'ENTER AX, AY:'
      READ (*,*,IOSTAT=IE) AX, AY
      IF (IE.NE.0) THEN
	 PRINT *, 'OOPS!'
	 GOTO 10
      ENDIF

   20 PRINT *, 'ENTER BX, BY:'
      READ (*,*,IOSTAT=IE) BX, BY
      IF (IE.NE.0) THEN
	 PRINT *, 'WHAT?'
	 GOTO 20
      ENDIF

C COMPUTE THE DOT PRODUCT

      THA = ATAN2(AY, AX)
      THB = ATAN2(BY, BX)
      THETA = ABS(THA - THB)

      ABDOT = SQRT(AX**2 + AY**2) * SQRT(BX**2 + BY**2) * COS(THETA)

      DOT = AX * BX + AY * BY

      PRINT *, 'IF I COMPUTE THE ANGLE, THEN THE DOT..', ABDOT
      PRINT *, 'OR, BY COMPONENTS..                   ', DOT

      END