Cumulative Maxima and Minima
DESCRIPTION:
Returns a vector of non-decreasing (resp. non-increasing) numbers which are the cumulative maxima (resp. minima) of the values in x.
USAGE: 
cummax(x)
cummin(x)
REQUIRED ARGUMENTS:
x:
a numeric vector.
Missing values (NA) are allowed.
VALUE:
a vector like x in which the ith element is the maximum (resp. minimum) of the first through the ith elements of x.
DETAILS:
If the first NA is x[j], then the jth and all following elements of the result will be NA.
SEE ALSO:
cumsum , max , pmax , peaks .
EXAMPLES: 
# compute times between subsequent maxima
set.seed(30)            #set the .Random.seed
x <- rnorm(100)
xm <- cummax(x)
diff((2:100)[xm[2:100]>xm[1:99]]) # returns c(5, 19, 41)