Return the index of the contract expiration date. The third Friday of the
month for options, the last third Friday of the quarter for futures.
Usage
options.expiry(x)
futures.expiry(x)
Value
A numeric vector of values to index on.
Arguments
x
a time-indexed zoo object
Author
Jeffrey A. Ryan
Details
Designed to be used within a charting context via addExpiry, the values returned
are based on the description above. Exceptions, though rare, are not accounted for.