“…For first-order polynomial models, orthogonal LHDs are useful because they ensure the estimates of linear effects are uncorrelated. Construction of orthogonal LHDs has been widely studied, see e.g., Ye (1998), Steinberg and Lin (2006), Cioppa and Lucas (2007), Bingham, Sitter, and Tang (2009), Pang, Liu, and Lin (2009), Georgiou (2009), Lin, Mukerjee, and Tang (2009), Lin (2009, 2010), Lin et al (2010), Sun, Pang, and Liu (2011), Georgiou and Stylianou (2011) (and its corrigendum Georgiou and Stylianou (2012)), Yang and Liu (2012), and Georgiou and Efthimiou (2014), among others. Note that some of them considered LHDs with fold-over structures, which makes sure that the sum of elementwise product of any three columns is zero.…”