; The start of every program must be preceeded by "PRO" and the file name must end in .pro
PRO align
JMAX = 80
EX = 0.0
DEX = 0.1
; Arrays must be declared as to the type of values they contain as well as how many elements in each dimension
; I believe floats are precise to the 6th decimal point, perhaps not as precise as a real in fortran. If necessary use a
; DblArr() instead of the FltArr().
Y1 = FLTARR(JMAX)
Y2 = FLTARR(JMAX)
Y3 = FLTARR(JMAX)
Y4 = FLTARR(JMAX)
Y5 = FLTARR(JMAX)
XP = FLTARR(JMAX)

; This is a for loop which seems to be a cross between C and Fortran syntax.
; IMPORTANT: IDL is like C in that it the 1st element is numbered "0", so the loop must only go to JMAX-1
FOR j = 0,JMAX-1 DO BEGIN
      X1=EX
      X2=EX/2
      X3=EX/3
      X4=EX/4
      X5=EX/5
      Y1[j]=X1*(2+X1)/((1+X1)*(1+X1))
      Y2[j]=X2*(2+X2)/((1+X2)*(1+X2))
      Y3[j]=X3*(2+X3)/((1+X3)*(1+X3))
      Y4[j]=X4*(2+X4)/((1+X4)*(1+X4))
      Y5[j]=X5*(2+X5)/((1+X5)*(1+X5))
      XP[j]=EX
      EX = EX + DEX
; Here I have put in just a couple of print statements to assure myself that the program is working properly
; Note the syntax, like all in IDL, is a comma after the command, then the variable to be acted upon.
; Multiple variables can be strung together with commas, but they won't start a newline that way.
      print, j
      print, XP
      print, ' '   ; There may be a better way, but I forced a line skip by printing a string with nothing but a space in it
ENDFOR

; Now we actually plot the arrays. In this case, XPis plotted on the X axis, and Y1 is on the Y axis.
: Remember that the dollar sign is used to indicate this in one giant statement.
      PLOT, XP, Y1, $
      XTITLE = 'INCIDENT ENERGY (EV)', $   ; This is the x axis label
      YTITLE = 'T TO V EFFICIENCY', $           ; This is the y axis label
      PSYM = 0, $   ; PSYM is the plotting symbol. In this case, there it is a line with no individual points.
      XSTYLE = 1, XRANGE = [0,8], $                ; The x axis is forced to the value specified in XRange
      YSTYLE = 1, YRANGE = [0,1], $                ; The y axis is forced to the value specified in YRange
      XTICKS = 4, XMINOR = 10, $                     ; There are 4 units between the XRange 0-8, i.e. ending at 2,4,6,&8
      YTICKS = 10, $                                              ; The Y axis does not have minor tick marks between the majors
      CHARSIZE = 1                                               ; A character size of 1 is the default and does not need to be specified

      OPLOT, XP, Y2                 ; This command overlays another plotted line over the first one
      OPLOT, XP, Y3
      OPLOT, XP, Y4
      OPLOT, XP, Y5

; I have removed the print command from this program to keep it simple. Look at the other examples of how to print

END