PROGRAM Lens

! Copyright 2006 Matthew Norton
!
!    This program is free software; you can redistribute it and/or modify
!    it under the terms of the GNU General Public License as published by
!    the Free Software Foundation; either version 2 of the License, or
!    (at your option) any later version.
!
!    This program is distributed in the hope that it will be useful,
!    but WITHOUT ANY WARRANTY; without even the implied warranty of
!    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
!    GNU General Public License for more details.
!
!    You should have received a copy of the GNU General Public License
!    along with this program; if not, write to the Free Software
!    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
!
! NOTE: This is in FORTRAN 90 and you will need a FORTRAN 90 complier to run this code
! --------------------------------------------------------------------------
!
! This Program solves the thin lens equation for the object location, the
! image location, or the focal length.
!
! --------------------------------------------------------------------------
!
! Created by Matthew S. Norton
! Created on March 23, 2006
! Created because I was bored
!
! --------------------------------------------------------------------------

IMPLICIT NONE

DOUBLE PRECISION Obj, Img, Foc
CHARACTER (1) :: Response

Main: DO
   PRINT *, "Do you want to solve for the object location (o), image location (i), or focal length (f) or enter 0 to quit?"
   READ *, Response

   SELECT CASE(Response)
   CASE("o")
      CALL OBJECT
   CASE("O")
      CALL OBJECT
   CASE("i")
      CALL IMAGE
   CASE("I")
      CALL IMAGE
   CASE("f")
      CALL FOCAL
   CASE("F")
      CALL FOCAL
   CASE ("0")
      EXIT Main
   CASE DEFAULT
      PRINT '(1X, A21, 1X, A1, 1X, A23)', "ERROR! Improper input,", Response, "please input o, i, or f"
      CYCLE Main
   END SELECT

END DO Main
CONTAINS

SUBROUTINE Object

  PRINT *, "What is the image distance?"
  READ *, Img
  PRINT *, "What is the focal length?"
  READ *, Foc

  Obj = (- Foc * Img) / (Foc - Img)

  PRINT '(1X, A, 1X, F10.6)', "The object distance is:", Obj
END SUBROUTINE Object

SUBROUTINE Image

  PRINT *, "What is object distance?"
  READ *, Obj
  PRINT *, "What is the focal length?"
  READ *, Foc

  Img = (-Foc * Obj) / (Foc - Obj)

  PRINT '(1X, A, 1X, F10.6)', "The image distance is:", Img

END SUBROUTINE Image

SUBROUTINE Focal

  PRINT *, "What is the object distance?"
  READ *, Obj
  PRINT *, "What is the image distance?"
  READ *, Img

  Foc = (Img * Obj) / (Img + Obj)

  PRINT '(1X, A, 1X, F10.6)', "The focal length is:", Foc
END SUBROUTINE Focal

END PROGRAM Lens