Real Analysis/Total Variation

Let f be a continuous function on an interval [a,b]. A partition of f on the interval [a,b] is a sequence xk such that a=x0< x1 <...< xk-1 < xk < ...xn=b. The total variation t of a function on the interval [a,b] is the supremum

t= sup{$$ \sum_{k=1}^{n} |f(x_k)-f(x_{k-1})| $$ : xk is a partition of [a,b]}.

If this supremum exists, then the function is of bounded variation on [a,b]. If a real function is of bounded variation over its whole domain, then it is called a function of bounded variation.