{smcl}
{* 8feb2008; rev, 2apr2008,2012feb9}
{hline}
help for {hi:covariancemat}
{hline}

{title:Generate a matrix of covariances}

{p 8 17 2}
{cmd:covariancemat}
{it:varlist} [{cmd:if} {it:exp}] [{cmd:in} {it:range}]
[{it:weight}]{cmd:, covarmat(}{it:mat}{cmd:)}


{title:Description}

{p 4 4 2}
{cmd:covariancemat} generates a matrix of the covariances of the
variables in {it:varlist}. The result is a square p-by-p matrix, where p is
the number of variables in {it:varlist}.

{p 4 4 2}
{cmd:aweight}s, {cmd:fweight}s, {cmd:pweight}s, and {cmd:iweight}s are allowed; {cmd:aweight}
is the default. See help {help weights}.

{p 4 4 2}
{cmd:covariancemat} was written for use by {help mahapick},
{help mahascore}, and {help mahascores}, but may be of use
in other circumstances.


{title:Options}

{p 4 4 2}
{cmd:covarmat(}{it:mat}{cmd:)} is required; it specifies the name of the matrix
to be created. If {it:mat} already exists as a scalar or matrix, it will be
overwritten. The row- and column names of {it:mat} will be the variable names
in {it:varlist}.


{title:Remarks}

{p 4 4 2}
Since the covariances are computed together, they are necessarily computed on the
set of observations that are nonmissing for all variables in {it:varlist}.
Thus, the results may differ from pairwise computations of covariances,
depending on the presence of missing values.
(This corresponds to the {cmd: common} option of {help variancemat} of the
mahapick package.)

{p 4 4 2}
This partly replicates functionality and borrows some code from {cmd:corrmat}
by Shannon Driver of Stata Corporation.


{title:Examples}

{p 4 8 2}
{cmd:. covariancemat age income numkids, covarmat(m)}

{p 4 8 2}
{cmd:. covariancemat age income numkids if numkids>0 [aw= wgt1], covarmat(m)}


{title:Author}
{p 4 4 2}
David Kantor.
Email {browse "mailto:kantor.d@att.net":kantor.d@att.net} if you observe any
problems.


{title:Also See}
{p 4 4 2}
{help mahapick}, {help mahascore}, {help mahascores}, {help mahascore2}, {help screenmatches},
{help variancemat}, {help stackids}.
See mahapick.ado for another example of the use of {cmd:covariancemat}.
