pro mtraj_selectdata,start,ndays,dayfracs,forward=forward
;+
; NAME:
;    mtraj_selectdata
; PURPOSE:
;    select files to be used by the trajectory model (see trajmain2)
; CATEGORY:
;    trajectory
; CALLING SEQUENCE:
;    mtraj_selectdata,start,ndays,datearray,$
;    forward=forward,dir=direc
;
; INPUTS:
;     start = start day number from the year 1900, fractions of 
;             the day are included
;     ndays = number of days of integration
; OPTIONAL INPUT PARAMETERS:
; KEYWORD PARAMETERS:
; OUTPUTS:
; OPTIONAL OUTPUT PARAMETERS:
; COMMON BLOCKS:
; SIDE EFFECTS:
; RESTRICTIONS:
; PROCEDURE:
; REQUIRED ROUTINES:
;     df_bestfile, day1900, date1900
; MODIFICATION HISTORY:
;    created mrs, 2/19/92, converted to use 
;   date1900 5/25/92
;   1999-11-29:nash:added avespec
;   $Header: /science/trajectory/programs/traj_selectdata.pro,v 1.25 1996/11/26 13:53:30 schom Exp $
;-

 err=0
  s=size(start)
  if s(n_elements(s)-2) eq 7 then dayni=day1900(start) else dayni=start

  f=forward 

  if f eq -1 then daystart=long(dayni)+1 else daystart=long(dayni)-1

; daystart is the starting date for data from the year 1900

 dayend=long(dayni)+long(f*ndays)+f ; this is the maximum ending date

; dayend is the ending date for data from the year 1900, note for backward trajectories
;    dayend is before daystart

; get data string arrays

icyce=0
icycf=0
xtend:
n=abs(daystart-dayend)
dayfracs=fltarr(n+1)
j=-1
if daystart lt dayend then begin
for val=daystart,dayend do begin
    j=j+1
    dayfracs(j)=val
    endfor
   endif else begin
for val=dayend,daystart do begin
    j=j+1
    dayfracs(j)=val
    endfor
endelse



return
end