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: lbfgs.m
    path of file: ./repos/voc-dpm/external/minConf/minFunc
    
    the code of the file until where you have to start completion: function [d] = lbfgs(g,s,y,Hdiag)

    
function [d] = lbfgs(g,s,y,Hdiag)
% BFGS Search Direction
%
% This function returns the (L-BFGS) approximate inverse Hessian,
% multiplied by the gradient
%
% If you pass in all previous directions/sizes, it will be the same as full BFGS
% If you truncate to the k most recent directions/sizes, it will be L-BFGS
%
% s - previous search directions (p by k)
% y - previous step sizes (p by k)
% g - gradient (p by 1)
% Hdiag - value of initial Hessian diagonal elements (scalar)

[p,k] = size(s);

for i = 1:k
    ro(i,1) = 1/(y(:,i)'*s(:,i));
end