1045 search results for "LaTeX"

Le Monde puzzle [#783]

July 20, 2012
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Le Monde puzzle [#783]

In a political party, there are as many cells as there are members and each member belongs to at least one cell. Each cell has five members and an arbitrary pair of cells only shares one member. How many members are there in this political party? Back to the mathematical puzzles of Le Monde (science

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Volatility and Correlation

July 19, 2012
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Volatility and Correlation

The implied option volatility reflects the price premium an option commands. A trader’s profit and loss ‘P&L’ from hedging option positions is driven to a large extend by the actual historical volatility of the underlying assets. Thus as option premiums … Continue reading →

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A weighting function for ‘nls’ / ‘nlsLM’

July 19, 2012
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A weighting function for ‘nls’ / ‘nlsLM’

Standard nonlinear regression assumes homoscedastic data, that is, all response values are distributed normally.  In case of heteroscedastic data (i.e. when the variance is dependent on the magnitude of the data), weighting the fit is essential. In nls (or nlsLM of the minpack.lm package), weighting can be conducted by two different methods: 1) by supplying

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Video: knitr, R Markdown, and R Studio: Introduction to Reproducible Analysis

July 19, 2012
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This post presents the video of a talk that I presented in July 2012 at Melbourne R Users on using knitr, R Markdown, and R Studio to perform reproducible analysis. I also provide links to a github repository where the R markdown examples can be examin...

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Dynamical systems: Mapping chaos with R

July 13, 2012
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Dynamical systems: Mapping chaos with R

Chaos. Hectic, seemingly unpredictable, complex dynamics. In a word: fun. I usually stick to the warm and fuzzy world of stochasticity and probability distributions, but this post will be (almost) entirely devoid of randomness. While chaotic dynamics are entirely deterministic, their sensitivity to initial conditions can trick the observer into seeing iid. In ecology, chaotic

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Representation of numerical NA’s in R and the 1954 enigma

July 8, 2012
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Representation of numerical NA’s in R and the 1954 enigma

I've always wondered how exactly the missing value (NA) in R is represented under the hood. Last weekend I was working on a little project that gave me enough excuse to spend some time on finding this out. So, I … Continue reading →

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Validating email adresses in R

July 5, 2012
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I currently program an automated report generation in R – participants fill out a questionnaire, and they receive a nicely formatted pdf with their personality profile. I use knitr, LaTex, and the sendmailR package. Some participants did not provide valid email addresses, which caused the sendmail function to crash. Therefore I wanted some validation of

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Rchievement of the day #3: Bloggin’ from R

July 1, 2012
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Rchievement of the day #3: Bloggin’ from R

I have become a complete knitr addict of late and have been using it in combination with RStudio’s R markdown support on a regular basis. In fact I wrote this post using it! It then dawned on me how great it would be if I … Continue reading →

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reproducible documents/analytics in R: the knitr package

June 26, 2012
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reproducible documents/analytics in R: the knitr package

When I am working in new institutions and I am asking: “Do you have a document management system?” I often get the answer:”Yap, we are using folders” … OKAY. Making analysis, developing applications and keeping an eye on code, data and applications make this even harder as it has to be. Of course not many

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