Trailing moving correlations (ignore NAs).
n-period trailing moving Pearson product moment correlations between a pair of variables, with d.f. correction, ignoring NAs.
Syntax:		@mcor(x, y, n)
	x:	series
	y:	series
	n	integer, series
Return:		series
For each observation 

 and integer 

, compute the correlations () using the current and previous 

 observations of the series,
and ignoring missing values (NAs).
If 
n is not an integer, the integer floor 

 will be used.
Examples
show @mcor(x, y, 12)
produces a linked series of the moving population correlation of the series x and y where NAs are ignored.
Cross-references
See also 
    
@mcov for NA-excluding trailing moving covariances
For the NA-propagating variant of this function, see 
    
@movcor.