You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: VBA_guessHyperpriors.m
    path of file: ./repos/VBA-toolbox/utils
    
    the code of the file until where you have to start completion: function [a, b] = VBA_guessHyperpriors (y, rangeEV)
% // VBA toolbox //////////////////////////////////////////////////////////
%
% [a, b] = VBA_guessHyperpriors (y, rangeEV)
% propose shape and scale parameters to use as hyperpriors for the
% measurement noise precision, based on the part of the variance one can
% expect the model to explain.
%

    
function [a, b] = VBA_guessHyperpriors (y, rangeEV)
% // VBA toolbox //////////////////////////////////////////////////////////
%
% [a, b] = VBA_guessHyperpriors (y, rangeEV)
% propose shape and scale parameters to use as hyperpriors for the
% measurement noise precision, based on the part of the variance one can
% expect the model to explain.
%
% IN:
%   - y: data to be fitted
%   - rangeEV: range of the fraction of variance to be explained. 
%       default = [0.1, 0.9], .ie between 10% and 90% of the total variance
% OUT:
%   - a, b: shape and scale parameters of the Gamma hyperprior
%
% /////////////////////////////////////////////////////////////////////////


%% check parameters
% =========================================================================
% fill in defaults
if nargin == 1
    rangeEV = [0.1, 0.9];
end