  function ris = risqrt (x, x0)
% function ris = risqrt (x, x0)
% Computes integrand to be used with function risint
% A gaussian distribution with an rms halfwidth of 1/2 wavelength
% is used for the squared refractive index distribution,
% approaching 1 far from the waveguide,
% and equal to 2 at the center of the waveguide.
% Input:  
%  x   array of positions where integrand is computed, 
%      measured in units of vacuum wavelength
%  x0  position where integration interval ends in function risint
% Output: 
%  ris array of corresponding values for the integrand
%

ris  =  sqrt (abs(normpdf(x, 0, 0.5) - normpdf(x0, 0, 0.5))./normpdf(0, 0, 0.5));
return
