SAS

Blogs on the SAS software

The next power of 2 and other tricks with logarithms

October 31, 2014
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The next power of 2 and other tricks with logarithms

The other day I was doing some computations that caused me to wonder, "What is the smallest power of 2 that is greater than a given number?" The mathematics is straightforward. Given a number n, find the least value of k such that 2k ≥ n or, equivalently, k ≥ […]

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How to use frequency analysis to crack the Cryptoquote puzzle

October 29, 2014
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How to use frequency analysis to crack the Cryptoquote puzzle

Many people enjoy solving word games such as the daily Cryptoquote puzzle, which uses a simple substitution cipher to disguise a witty or wise quote by a famous person. A common way to attack the puzzle is frequency analysis. In frequency analysis you identify letters and pairs of letters (bigrams) […]

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Video: Using heat maps to visualize matrices

October 27, 2014
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Video: Using heat maps to visualize matrices

One of my presentations at SAS Global Forum 2014 was about the new heat map functions in SAS/IML 13.1. Over the summer I created a short video of my presentation, which gives an overview of visualizing matrices with heat maps, and describes how to choose colors for heat maps: If […]

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Does this kurtosis make my tail look fat?

October 22, 2014
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Does this kurtosis make my tail look fat?

What is kurtosis? What does negative or positive kurtosis mean, and why should you care? How do you compute kurtosis in SAS software? It is not clear from the definition of kurtosis what (if anything) kurtosis tells us about the shape of a distribution, or why kurtosis is relevant to […]

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Example 2014.12: Changing repeated measures data from wide to narrow format

October 21, 2014
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Example 2014.12: Changing repeated measures data from wide to narrow format

Data with repeated measures often come to us in the "wide" format, as shown below for the HELP data set we use in our book. Here we show just an ID, the CESD depression measure from four follow-up assessments, plus the baseline CESD. Obs ID CESD...

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Compute the log-determinant of an arbitrary matrix

October 20, 2014
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Compute the log-determinant of an arbitrary matrix

A few years ago I wrote an article that shows how to compute the log-determinant of a covariance matrix in SAS. This computation is often required to evaluate a log-likelihood function. My algorithm used the ROOT function in SAS/IML to compute a Cholesky decomposition of the covariance matrix. The Cholesky […]

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Compute the log-determinant of an arbitrary matrix

October 20, 2014
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Compute the log-determinant of an arbitrary matrix

A few years ago I wrote an article that shows how to compute the log-determinant of a covariance matrix in SAS. This computation is often required to evaluate a log-likelihood function. My algorithm used the ROOT function in SAS/IML to compute a Cholesky decomposition of the covariance matrix. The Cholesky […]

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Wolfram’s Rule 30 in SAS

October 17, 2014
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Wolfram’s Rule 30 in SAS

My previous blog post describes how to implement Conway's Game of Life by using the dynamically linked graphics in SAS/IML Studio. But the Game of Life is not the only kind of cellular automata. This article describes a system of cellular automata that is known as Wolfram's Rule 30. In […]

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Cellular automata and the Game of Life in SAS

October 15, 2014
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Cellular automata and the Game of Life in SAS

A colleague jokingly teases me whenever I write a blog that demonstrates how to write fun and exciting programs by using SAS software. "Why do you get to have all the fun?" he mock-chides. Today I'm ready to face his ribbing, because this article is about Conway's Game of Life […]

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Fat-tailed and long-tailed distributions

October 13, 2014
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Fat-tailed and long-tailed distributions

The tail of a probability distribution is an important notion in probability and statistics, but did you know that there is not a rigorous definition for the "tail"? The term is primarily used intuitively to mean the part of a distribution that is far from the distribution's peak or center. […]

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