Editing Design matrix (section)

==Size==
The design matrix has dimension ''n''-by-''p'', where ''n'' is the number of samples observed, and ''p'' is the number of variables ([[Feature (machine learning)|features]]) measured in all samples.<ref>{{cite book |last1=Johnson |first1=Richard A |last2=Wichern |first2=Dean W |date=2001 |title=Applied Multivariate Statistical Analysis |publisher=Pearson |pages=111–112 |isbn=0131877151 }}</ref><ref>{{cite web|title=Basic Concepts for Multivariate Statistics p.2|url=https://support.sas.com/publishing/pubcat/chaps/56902.pdf |publisher=SAS Institute}}</ref>

In this representation different rows typically represent different repetitions of an experiment, while columns represent different types of data (say, the results from particular probes).  For example, suppose an experiment is run where 10 people are pulled off the street and asked 4 questions.  The data matrix ''M'' would be a 10×4 matrix (meaning 10 rows and 4 columns).  The datum in row ''i'' and column ''j'' of this matrix would be the answer of the ''i'' <sup>th</sup> person to the ''j'' <sup>th</sup> question.