Blog Archives

Temperature reconstruction with useless proxies

May 25, 2012
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Temperature reconstruction with useless proxies

In a number of previous posts I considered the temperature proxies that have been used to reconstruct global mean temperatures during the past millenium. In this post I want to show how such a temperature reconstruction would look like if the proxies had no relation at all to the actual temperatures. The motivation is the

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Inferring the community structure of networks

May 21, 2012
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Inferring the community structure of networks

I continue my little excursion into network science. In the last post, I gave a little introduction to simulating and visualizing undirected networks with community structure in R. In this post I want to explore a method to infer the community structure of a network from its adjacency matrix. That is, given that I know

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A minimal network example in R

May 18, 2012
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A minimal network example in R

Network science is potentially useful for certain problems in data analysis, and I know close to nothing about it. In this short post I present my first attempt at network analysis: A minimal example to construct and visualize an artificial undirected network with community structure in R. No network libraries are loaded. Only basic R-functions

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Spurious correlations and the Lasso

May 13, 2012
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Spurious correlations and the Lasso

Autocorrelation of a time series can be useful for prediction because the most recent observation of the prediction target contains information about future values. At the same time autocorrelation can play tricks on you because many standard statistical methods implicitely assume independence of measurements at different times. The correlation coefficient between two variable and has

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Discovering power laws and removing “shit”

May 10, 2012
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Discovering power laws and removing “shit”

Imagine you perform a statistical analysis on a time series of stock market data. After some transformation, averaging, and “renormalization” you find that the resulting quantity, let’s call it , behaves as a function of time like . Since you are a physicist you get excited because you have just discovered a power law. Physicists

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The hockeystick revisited

May 7, 2012
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The hockeystick revisited

Previous posts: Correlation of temperature proxies with observations The “best” proxies for temperature reconstruction Okay, I couldn’t resist. I wanted to provide some more in depth analysis of temperature proxies, but I just went ahead and did my own little reconstruction of Northern hemisphere annual average temperatures over the past millenium using McShane et al.‘s

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The “best” proxies for temperature reconstruction

April 29, 2012
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The “best” proxies for temperature reconstruction

In the last post I presented the distribution of correlation coefficients of temperature proxies with the actual temperature observations during the past 150 years. One of the conclusions was that most proxies correlate weakly with temperature observations. However, there seemed to be some proxies that do have some significant positive correlation with the observations. These

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Correlation of temperature proxies with observations

April 28, 2012
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Correlation of temperature proxies with observations

The climate change debate focuses mainly around the assumption that the annual global mean temperatures of the past few decades have been the highest in the past millenium. How do we know what the annual global mean temperature was in the year, say, 1351 AD? The answer is: Through temperature proxies. Such proxies include tree

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Complex arithmetic and airplane wings

April 23, 2012
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Complex arithmetic and airplane wings

I was once told that the reason that such a shape was so commonly used for aeroplane wings was merely that then one could study it mathemtically by just employing the Zhoukowski transformation. I hope that this is not true! (R. Penrose, “The Road to Reality”, p.150) Penrose here talks about a complex holomorphic mapping

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Phase space plot of the kicked rotor

April 21, 2012
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Phase space plot of the kicked rotor

In the idealized physical world, a rotor is simply a mass attached to an axis of length , free to move in the plane. Gravity and friction are absent. Such a rotor becomes a kicked rotor if it is periodically hit with a hammer. Every kick transfers momentum to the rotor and the time between

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