Function Toler, x, type = typ, double = dob

;+
; NAME:
;	TOLER
; VERSION:
;	3.0
; PURPOSE:
;	Establishes numerical tolerance value for numerical procedures.
; CATEGORY:
;	Programming.
; CALLING SEQUENCE:
;	Result = TOLER(X [, keywords])
; INPUTS:
;    X
;	Numeric, otherwise arbitrary.  Ignored if one of the keywords TYPE or
;	DOUBLE (see below) is used.
; OPTIONAL INPUT PARAMETERS:
;	None.
; KEYWORD PARAMETERS:
;    TYPE
;	Numeric type code.  If given overrides the type provided by X.
;    /DOUBLE
;	Switch.  Specifies double precision.  If given, overrides both TYPE and
;	the type provided by X.
; OUTPUTS:
;	Returns a value equal to twice the .EPS field of the structure created 
;	by the IDL function MACHAR.  If the type code, as set by the type of X, 
;	or directly by one of the keywords TYPE or DOUBLE is 5 (DOUBLE) or 9 
;	(DOUBLECOMPLEX), MACHAR is called with the keyword /DOUBLE.
; OPTIONAL OUTPUT PARAMETERS:
;	None.
; COMMON BLOCKS:
;	None.
; SIDE EFFECTS:
;	None.
; RESTRICTIONS:
;	X (when provided) must be numeric else an error occurs.  Similarly, 
;	calling TOLER with TYPE = 8 or 9 will cause an error.
; PROCEDURE:
;	Straightforward.  Uses MACHAR.  Calls DEFAULT and TYPE from MIDL.
; MODIFICATION HISTORY:
;	Created 15-JUN-1995 by Mati Meron.
;	Modified 10-SEP-1998 by Mati Meron.  Added keyword /DOUBLE.
;-

    on_error, 1
    nonum = [7,8,10,11,12,13,14,15]
    if keyword_set(dob) then typ = 5 else typ = Default(typ,Type(x))
    if (where(nonum eq typ))(0) ge 0 then message, 'input must be numeric!'
    eps = Machar(double = typ eq 5 or typ eq 9)
    return, eps.eps
end