;+
;
; @file_comments
; project linearly a segment, a vector whose boundaries are [a,b] on
; a vector whose boundaries are [c,d]
;
; @categories
; Calculation
;
; @param VECTEUR {type=vector}
; A vector whose the first element must be the smallest one and the last must be the biggest one.
;
; @param BORNES
; New boundaries of the vector.
;
; @keyword MP
; Activate this keyword to the function send back this a vector of 2
; elements which are the m and p of the linear projection y=mx+p used
; to pass from the [a,b] segment to the [c,d] segment.
;
; @returns
; A vector whose new boundaries are specified by BORNES.
;
; @examples
;
;   IDL> a=indgen(9)
;   IDL> print, a
;          0       1       2       3       4       5       6       7       8
;   IDL> print, projsegment(a,[0,80])
;          0      10      20      30      40      50      60      70      80
;   IDL> print, projsegment(a,[0,-80])
;          0     -10     -20     -30     -40     -50     -60     -70     -80
;   IDL> print, projsegment(a,[-80,0])
;        -80     -70     -60     -50     -40     -30     -20     -10      0
;
; @history
; Sebastien Masson (smasson\@lodyc.jussieu.fr)
;                       24/6/1999
;
; @version
; $Id$
;
;-
;
FUNCTION projsegment, vecteur, bornes, MP = mp
;
  compile_opt idl2, strictarrsubs
;
   a1 = float(vecteur[0])
   b1 = float(vecteur[n_elements(vecteur)-1])
   a2 = float(bornes[0])
   b2 =float( bornes[1])
   if a1 EQ b1 then return, -1
   m = (b2-a2)/(b1-a1)
   p = a2-m*a1
;--------------------------------------------------------------
   if keyword_set(mp) then return, [m, p] ELSE return, m*vecteur+p
;--------------------------------------------------------------
end