Old Posts Tagged with "rwt-pending"

These are Blog Archives
Here you can find links to old content I had on the blog, prior to switching to our group pages. Have fun looking around... some of it is pretty good! If you are looking for the best of the best posts from both the old and new eras, then go to the Articles Page. If you want the newest material, browse the public group (and the google waves associated with it).

The Purpose of Science

Posted on September 21st, 2009
Written by Richard

People have funny ideas about science. They seem to think it is about uncovering the truth, but that’s not really correct. From Wikipedia:
“Science refers in its broadest sense to any systematic knowledge-base or prescriptive practice that is capable of resulting in a prediction or predictable type of outcome.”
One philosophical abyss you must eventually [...]

The EMA and RC Circuits

Posted on September 17th, 2009
Written by Richard

In this installment of my series on the Exponential Moving Average, I point out the relationships between the EMA and simple analog RC circuits. Electronics really isn’t my thing, but I found this to be interesting and kinda beautiful.

More Thoughts on “Free” in the Digital Age

Posted on September 13th, 2009
Written by Richard

Wow, this guy has been studying the exact topic I’ve been struggling with lately. Remember recently I was contemplating the way digital products defy valuation? Chris Anderson just put out a book, Free: The Future of a Radical Price. Here’s a talk he gave on the subject for the Wired Business [...]

How Well Do EMAs Track Parabolic Curves?

Posted on September 7th, 2009
Written by Richard

In the last post, we went over how well EMAs track straight lines in detail. Now, it’s natural to wonder how EMAs do with sources modeled after:
s[t] = m t^2
It turns out, they don’t do very well at all. Here’s our standard 20-ema of the basic parabola with ‘m’ = 1:

As you can [...]

How Well Do EMAs Track Straight Lines?

Posted on September 5th, 2009
Written by Richard

We know from a couple posts ago that the EMA of a constant is equal to that constant. In other words, EMA’s track a DC signal perfectly. It might be natural to wonder how well they do against a straight line.
Recall that a line has a slope ‘m’ and an offset ‘b’ at [...]

The Exponential Moving Average is Invertible

Posted on September 4th, 2009
Written by Richard

I never noticed this until today, but the EMA filter is 100% invertible. That means, if you give me an ema-smoothed dataset, I can tell you what the original dataset was. You would think, as a low-pass filter, that it would be throwing away the high-frequency data, but it’s not. It’s just [...]

A Few Algebraic Properties of EMAs

Posted on September 3rd, 2009
Written by Richard

Here are a few algebraic properties of EMAs:

ema(constant) = constant
ema(s + t) = ema(s) + ema(t)
ema(s + constant) = ema(s) + constant
ema(s * constant) = ema(s) * constant
ema1(ema2(s)) = ema2(ema1(s))

Also, recall that the standard ‘bar form’ of an EMA, such as when we say “20-ema,” is actually specifying the ema [...]

Initial Value of an EMA

Posted on September 1st, 2009
Written by Richard

The definition of an EMA:
ema[t] = (1-alpha)*ema[t-1] + alpha*data[t]
… tells you what to do with the last EMA you had and the current data sample. That’s all fine and good, but how do you get started? In other words, how do you get your first EMA value? The formula above is no [...]

The Welles Wilder MA

Posted on August 31st, 2009
Written by Richard

My EMA article will be as comprehensive as I can manage. I’m going to try to cover every facet of the EMA that I’ve heard of. If there are any topics you’d like to see covered, write them in as comments so I will be sure to include them. Here’s another [...]

EMA Accuracy After n Historical Bars

Posted on August 25th, 2009
Written by Richard

In case you can’t tell, I’m working on the mother of all EMA articles. A couple parts have been posted here so far. As I pointed out, my plan is to post bits on the blog prior to the article, for two reasons:

it keeps me moving forward, without the pressure of polishing the [...]

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