Quantile regression application on matlab

I'm using the code in the following link, https://it.mathworks.com/matlabcentral/fileexchange/70072-quantile-regression#feedbacks, but i have some issues when i click on run and i'm on Readme.m i got in the below error, what can i put as z?

>> Readme

Undefined function or variable 'z'.

Error in Readme (line 13)

[beta, p]=qr_standard([z x(:,i)], y, tau,'test','wald','method','interior');

[shubin ma]

函数不能直接运行，你需要创建主程序来调用这个函数，在readme.m里有一个example，你可以看一下