added check for missing n when ratio is specified to EMA. If missing,…

… converts n to approx. "correct" value given ratio

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/ttr/pkg@98 edb9625f-4e0d-4859-8d74-9fd3b1da38cb

R/MovingAverages.R

@@ -51,6 +51,11 @@ function (x, n=10, wilder=FALSE, ratio=NULL) {
   # Check for non-leading NAs
   # Leading NAs are handled in the C code
   x.na <- xts:::naCheck(x, n)
+
+  # If ratio is specified, and n is not, set n to approx 'correct'
+  # value backed out from ratio
+  if(missing(n) && !missing(ratio))
+    n <- trunc(2/ratio - 1)
 
   # Determine decay ratio
   if(is.null(ratio)) {