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Message from discussion Question on bounded variation functions
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miki  
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 More options Nov 7 2009, 7:01 pm
Newsgroups: sci.math
From: miki <miki.li...@gmail.com>
Date: Sat, 7 Nov 2009 11:01:25 -0800 (PST)
Local: Sat, Nov 7 2009 7:01 pm
Subject: Re: Question on bounded variation functions
On Nov 7, 4:18 pm, David C. Ullrich <dullr...@sprynet.com> wrote:

> On Sat, 7 Nov 2009 01:18:24 -0800 (PST), miki <miki.li...@gmail.com>
> wrote:

> >Hello All,

> >The well-known definition of bounded variation functions is about
> >their behavior on closed intervals.
> >To say, "The total variation of real-valued function f, defined on an
> >interval [a, b] belongs to R is the quantity V_a_b_(f) = sup(sum(|f(x_i
> >+1) - f(x_i)|)) of all partitions of the interval considered", (etc.)

> >My question is, can I use or define total variation for a half-open
> >interval, say, [a, b)?

> Yes.

> >In any case, my intention is to define (or use) the following: for any
> >eps > 0 the total variation of the function
> >f on the interval [a, b - eps] is finite. Is it the same as to say
> >that the total variation of a function over the half-open interval [a,
> >b) is finite?

> Of course not - the total variation on [a, b-eps] could be finite
> for every eps > 0 but tend to infinity as eps -> 0.

> If the total variation on [a,b-eps] is _bounded_ for eps > 0
> then the total variation on [a,b) is finite.

> >Regards,
> >Miki

> David C. Ullrich

> "Understanding Godel isn't about following his formal proof.
> That would make a mockery of everything Godel was up to."
> (John Jones, "My talk about Godel to the post-grads."
> in sci.logic.)

Thanks,

My question is, can I use or define total variation for a half-open

> >interval, say, [a, b)?

> Yes.

So, what is the definition of total variation on the interval [a, b)?
How can I write the sum if the left-end of the interval is open?

If I take the function f(x)=1/(x-5) for example,
it is of bounded variation on [4, 5 - e] for every e > 0 as long as e
does not tends to zero (so actually, its not for every e...)
OK, so what about saying that it is of bounded variation on [4, 5).
Now is it correct? If so, whats the meaning of it in terms of
total variation? how can I compute its total variation?

thanks
Miki


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