Blog Archives

The Wishart distribution: Covariance matrices for multivariate normal data

November 26, 2014
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The Wishart distribution: Covariance matrices for multivariate normal data

I've written about how to generate a sample from a multivariate normal (MVN) distribution in SAS by using the RANDNORMAL function in SAS/IML software. Last week a SAS/IML programmer showed me a program that simulated MVN data and computed the resulting covariance matrix for each simulated sample. The purpose of […]

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Overview of new features in SAS/IML 13.1

November 24, 2014
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Overview of new features in SAS/IML 13.1

SAS software contains a lot of features, and each release adds more.To make sure that you do not miss new features that appear in the SAS/IML language, the word cloud on the right sidebar of my blog contains numbers that relate to SAS or SAS/IML releases. For example, you can […]

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Resampling and permutation tests in SAS

November 21, 2014
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Resampling and permutation tests in SAS

My colleagues at the SAS & R blog recently posted an example of how to program a permutation test in SAS and R. Their SAS implementation used Base SAS and was "relatively cumbersome" (their words) when compared with the R code. In today's post I implement the permutation test in […]

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What is the coefficient of variation?

November 19, 2014
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What is the coefficient of variation?

I sometimes wonder whether some functions and options in SAS software ever get used. Last week I was reviewing new features that were added to SAS/IML 13.1. One of the new functions is the CV function, which computes the sample coefficient of variation for data. Maybe it is just me, […]

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The difference between RUN and CALL for SAS/IML subroutines

November 17, 2014
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The difference between RUN and CALL for SAS/IML subroutines

Have you ever noticed that some SAS/IML programmers use the CALL statement to call a subroutine, whereas others use the RUN statement? Have you ever wondered why the SAS/IML language has two statements that do the same thing? It turns out that the CALL statement and the RUN statement do […]

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The distribution of Pythagorean triples

November 12, 2014
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The distribution of Pythagorean triples

When I studied high school geometry, I noticed that many homework problems involved right triangles whose side lengths were integers. The canonical example is the 3-4-5 right triangle, which has legs of length 3 and 4 and a hypotenuse of length 5. The triple (3, 4, 5) is called a […]

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An efficient way to increment a matrix diagonal

November 10, 2014
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An efficient way to increment a matrix diagonal

I was recently asked about how to use the SAS/IML language to efficiently add a constant to every element of a matrix diagonal. Mathematically, the task is to form the matrix sum A + kI, where A is an n x n matrix, k is a scalar value, and I is the […]

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The distribution of blood types by country

November 7, 2014
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The distribution of blood types by country

My colleague Robert Allison has a knack for finding fascinating data. Last week he did it again by locating data about how blood types and Rh factors vary among countries. He produced a series of eight world maps, each showing the prevalence of a blood type (A+, A-, B+, B-, […]

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Binning data by quantiles? Beware of rounded data

November 5, 2014
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Binning data by quantiles? Beware of rounded data

In my article about how to create a quantile plot, I chose not to discuss a theoretical issue that occasionally occurs. The issue is that for discrete data (which includes rounded values), it might be impossible to use quantile values to split the data into k groups where each group […]

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Recent additions to the SAS/IML file exchange

November 3, 2014
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Recent additions to the SAS/IML file exchange

It has been three months since the introduction of the SAS/IML File Exchange, so I thought I'd give a short update on recent submissions and activity. The web site administrators have created an easy-to-remember shortcut to the File Exchange: http://communities.sas.com/sas-iml-file-exchange There have been eight new articles submitted to the File […]

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