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: g_VBvolatile0.m
    path of file: ./repos/VBA-toolbox/demos/_models
    
    the code of the file until where you have to start completion: function [gx] = g_VBvolatile0(x,P,u,in)
% computes the probability of the learner choosing 'a=1'.
% [gx] = g_VBvolatile0(x,P,u,in)
% This function derives the action emission law from the current belief of

    
function [gx] = g_VBvolatile0(x,P,u,in)
% computes the probability of the learner choosing 'a=1'.
% [gx] = g_VBvolatile0(x,P,u,in)
% This function derives the action emission law from the current belief of
% the learner. It is valid in an empirical context akin to a multiarmed
% bandit problem, whereby the learner is asked to bet on the outcome at
% each trial.
% Note: the state-space includes the first- and second- order moments of
% the log-odds probability that each action yield a reward, ie P(R|a).
% IN:
%   - x: the previous posterior sufficient statistics.
%   - P: the response model parameters vector:
%   P(1): temperature/utility scaling
%   P(2): preference bias towards choosing action a=1
%   - u: the current input to the learner.
%   - in: further quantities handed to the function.
% OUT:
%   - gx: the expected next input to the learner, according to its previous
%   updated belief about the hidden states.


switch in.respmod
    case 'taylor' % neglect uncertainty on P(R|a=1)
        x1 = x(2); % E[log-odds P(R|a=1)]
        x0 = x(7); % E[log-odds P(R|a=0)]
    case 'fixedForm' % account for uncertainty on P(R|a=1)
        a = 0.368;
        x1 = x(2)./sqrt(1+a*exp(x(3)));
        x0 = x(7)./sqrt(1+a*exp(x(8)));
    otherwise
        error(['Invalid or missing response model specification: ', respmod]);
end