;***********************************************************************
;
;*PROCDURE NAME:
;
;    GAUSS   (General IDL Library 01)  Aug 19, 1979
;
;*PURPOSE:
;
;    TO CALCULATE A GAUSSIAN FUNCTION
;
;*CALLING SEQUENCE:
;
;    GAUSS,X,X0,DX,YMAX,Y
;
;*PARAMETERS:
;
;    X     (REQ) (I) (0 1) (I L F D)
;          required scalar or vector containing the independent variable(s)
;
;    X0    (REQ) (I) (0)   (F D)
;          required scalar giving the center of the Gaussian function
;          This parameter must have the same units as X.
;
;    DX    (REQ) (I) (0)   (F D)
;          required scalar giving the one sigma width of the distribution
;          This parameter must have the same units as X.
;
;    YMAX  (REQ) (I) (0)   (F D)
;          the Gaussian value at the peak of the distribution
;
;    Y     (REQ) (O) (0 1) (F D)
;          required output scalar or vector giving the calculated value
;          of the gaussian from the expression:
;          Y = YMAX * EXP (-0.5 * ((X-X0)/DX)^2)
;
;***********************************************************************
 pro gauss,x,x0,dx,ymax,y
;
 npar = n_params(0)
 if npar eq 0 then begin
    print,' GAUSS,X,X0,DX,YMAX,Y'
    retall
 endif  ; npar
 parcheck,npar,5,'GAUSS'
 pcheck,x,1,110,0011
 pcheck,x0,2,100,0011
 pcheck,dx,3,100,0011
 pcheck,ymax,4,100,0011
 if dx ne 0 then begin
    arg=(abs((x-x0)/dx)<9.)   ; set values 9 sigma to 0 to avoid trap errors
    y=exp(-arg*arg/2)*(arg lt 9.0)
 endif else y=(0.*x)*(x ne x0)+(x eq x0) ; if dx eq 0 return delta function
 y=y*ymax
 return
 end  ; gauss