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Peakoil.com :: View topic - Price Prediction Based on the Periodicity Transform
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Price Prediction Based on the Periodicity Transform
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khebab
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PostPosted: Thu Jul 07, 2005 3:54 pm    Post subject: Price Prediction Based on the Periodicity Transform Add User to Ignore List Reply with quote

A little bit of fun with numbers:

If we look at the crude oil prices since Septermber 2003 (NYMEX), we can make the following observations:
- prices are on a upward linear trend
- prices fluctuations are somewhat periodic;

A new signal processing tool has been proposed recently by William Sethares called the Periodicity Transform:
Quote:
Periodicity Transforms decompose a data sequence into a sum of simple periodic sequences by projecting onto a set of periodic subspaces, leaving residuals whose periodicities have been removed. As the name suggests, this decomposition is accomplished directly in terms of periodic sequences and not in terms of frequency or scale, as do the Fourier and Wavelet Transforms. In consequence, the representation is linear-in-period, rather than linear-in-frequency or linear-in-scale. Unlike most transforms, the set of basis vectors is not specified a priori, rather, the Periodicity Transform finds its own "best" set of basis elements. Technically, the collection of all periodic subspaces forms a frame, a more-than-complete spanning set. The Periodicity Transforms specify ways of sensibly handling the redundancy by exploiting some of the general properties of the periodic subspaces


Check the following website for more details and some Matlab code:
William Sethares's Home Page

I propos to apply this tool to model the price "superspikes" that have been observed lately.

First, I estimate the linear trend by robust least-square regression:
Code:
Price= 28.2298 + 0.0418 * Days

Where days are the number of "Days" since September, 03 2003.

Then, I applied the periodicity transform on the regression residuals to extract the basic periodic basis composing the observed price fluctuations. I excluded the first 200 days from the data because they seem to have a different volatility pattern. I look for 8 basis, the figure below gives the 4 strongest ones:


The reconstructed residuals (sum of all the periodic basis) are shown below:




Forecasting

The price forecast uses the linear trend on which we add the periodic basis from the periodicity transform. This is the result:



The blue linear curve is the estimated linear trend. The dark points are the observed prices and the blue curve is the linear trend plus the periodic basis. We can see that we may pass $70 at the end of 2005 and $80 at the end of summer 2006. However, this model is unable to take into account the observed increase in volatility that is represented by the two blue dashed lines.

Of course, everything above is highly speculative! Smile
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Last edited by khebab on Thu Jul 07, 2005 6:51 pm; edited 1 time in total
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Jack
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PostPosted: Thu Jul 07, 2005 4:06 pm    Post subject: Add User to Ignore List Reply with quote

Fascinating! Thanks for doing the analysis.
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geoman
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PostPosted: Thu Jul 07, 2005 4:37 pm    Post subject: Add User to Ignore List Reply with quote

So according to your analysis, we are at a peak in prices right now. It looks lke prices will go back down to the low to mid fifties in the next couple of months then go back up.

It also looks like your model underestimated the price of oil a few months back. Could you explain that?
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VMA131Marine
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PostPosted: Thu Jul 07, 2005 4:41 pm    Post subject: Add User to Ignore List Reply with quote

Another comment: It appears that the amplitude of the fluctuations in price is increasing as the price gets high. However, your prediction keeps the amplitude constant. I would agree that it is not reasonable to let the amplitude grow without bounds but what will be the limiting factor in th future?
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khebab
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PostPosted: Thu Jul 07, 2005 6:44 pm    Post subject: Add User to Ignore List Reply with quote

geoman wrote:
So according to your analysis, we are at a peak in prices right now. It looks lke prices will go back down to the low to mid fifties in the next couple of months then go back up.

Yes, it looks like it, time will tell. I'm still playing with the parameters, in particular the number of periodic basis.
geoman wrote:

It also looks like your model underestimated the price of oil a few months back. Could you explain that?

I don't understand, there are no predictions back in time (by definition). Maybe you are talking about the two dashed blue lines which are very approximative right now, I'm still looking for a way to estimate price volatility.
VMA131Marine wrote:
Another comment: It appears that the amplitude of the fluctuations in price is increasing as the price gets high. However, your prediction keeps the amplitude constant. I would agree that it is not reasonable to let the amplitude grow without bounds but what will be the limiting factor in th future?

You're right. The periodicity transform cannot capture variations in scale (volatility). One possibility could be to multiply the fluctuations by a scaling factor which is increasing with time. This is what I tried to achieve with the two dashed lines.
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khebab
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PostPosted: Thu Jul 07, 2005 7:07 pm    Post subject: Add User to Ignore List Reply with quote

Tomorrow I will try to inject some scaling factor on the predicted fluctuations maybe based on a fit on the local variance of the residuals.

There is also a possibilty that the trend is in fact slightly exponential but the factor in the exponential is very very small which makes its estimation a little bit unreliable.
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RonMN
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PostPosted: Thu Jul 07, 2005 7:40 pm    Post subject: Add User to Ignore List Reply with quote

I don't mean to sound "flip"...

But do you really think that mathmatics can calculate human nature?

Whether we will "band together" or "fight a mad max senario" is beyond me...and i do believe it's beyond mathmatics as well.
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khebab
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PostPosted: Thu Jul 07, 2005 7:53 pm    Post subject: Add User to Ignore List Reply with quote

RonMN wrote:
But do you really think that mathmatics can calculate human nature?

Nope, any major events can mess up this little prediction model (Terrorist attack, Ghawar collapse, etc.). I just find that the linear trend fit pretty nicely with the data, nothing more. It's surprising that such a chaotic market is showing such a consistent long term trend.
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EnergySpin
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PostPosted: Thu Jul 07, 2005 8:02 pm    Post subject: Add User to Ignore List Reply with quote

Quote:
It's surprising that such a chaotic market is showing such a consistent long term trend.


You are using linear extrapolation!!! Shame on you!!!
Where is the non-linear convolution of hyper-exponential kernes?
Just kidding ... Rolling Eyes
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khebab
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PostPosted: Thu Jul 07, 2005 8:18 pm    Post subject: Add User to Ignore List Reply with quote

EnergySpin wrote:
You are using linear extrapolation!!! Shame on you!!!

I know, it's shocking! Very Happy
All the hard work is done by the periodicity transform which is a kind of non parameteric signal decomposition.
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EnergySpin
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PostPosted: Thu Jul 07, 2005 8:26 pm    Post subject: Add User to Ignore List Reply with quote

I feel stupid .... Shocked
Checked my HD for papers I am randomly selecting ... apparently hyperexponential kernels are used to fit "long tailed data".
So .... they should be good for at least the part of the curve prior to depletion (then it is down the cliff) Shock
BTW thanks for alerting me to this SP methodology. Has it been tried to denoise Black-Scholes stochastic processes?
Sounds pretty close to a wavelet based SP approach.
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khebab
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PostPosted: Thu Jul 07, 2005 8:33 pm    Post subject: Add User to Ignore List Reply with quote

EnergySpin wrote:
BTW thanks for alerting me to this SP methodology. Has it been tried to denoise Black-Scholes stochastic processes?
Sounds pretty close to a wavelet based SP approach.

I have not seen many applications yet except some musical data analyis. I don't think the basis is orthogonal and the projection operator is not equivalent to a linear filtering. I'm still in my learning curve with this new tool.
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MicroHydro
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PostPosted: Thu Jul 07, 2005 9:02 pm    Post subject: Add User to Ignore List Reply with quote

The baseline data represents a period of economic expansion with rapidly increasing demand and slowly increasing supply. Neither might be true in the near future. I would guess that both a recession (falling demand) and oil depletion (falling supply) are near at hand. Not clear which will come first, so impossible to predict future market conditions.
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khebab
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PostPosted: Thu Jul 07, 2005 9:33 pm    Post subject: Add User to Ignore List Reply with quote

MicroHydro wrote:
The baseline data represents a period of economic expansion with rapidly increasing demand and slowly increasing supply. Neither might be true in the near future. I would guess that both a recession (falling demand) and oil depletion (falling supply) are near at hand. Not clear which will come first, so impossible to predict future market conditions.

Agreed, so far demand has been strong which is the driving force of this market but not for long.
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BabyPeanut
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PostPosted: Thu Jul 07, 2005 9:40 pm    Post subject: Add User to Ignore List Reply with quote

Based on your chart the price will come down in August. Fat Chance! Laughing
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