.BG
.FN stop
.FN warning
.TL
Error and Warning Messages
.CS
stop(message)
warning(message)
.AG message
character string.
The function `stop' prints the name of the function
calling `stop' and  `message', and then terminates
execution of the current expression.
If `message' is omitted, the expression is terminated silently.
Function `warning' prints a similar warning message at the end of evaluation
of the expression, but does
not affect execution.
.SE
If too many warning messages are generated in one expression (currently more than
five), the messages
are stored together on a session object named `last.warning'.
Only the number of warnings is then printed.
The function `warnings' will print out the stored messages.
.SA
`warnings', `restart'.
.EX
warning(paste("Rank is",n,"should be",ncol(x)))
if(any(is.na(x))) stop("`NA's are not allowed in x")
.KW error
.WR
