Fast simulation of multivariate normal data with an AR(1) correlation structure

October 3, 2018
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Fast simulation of multivariate normal data with an AR(1) correlation structure

It is sometimes necessary for researchers to simulate data with thousands of variables. It is easy to simulate thousands of uncorrelated variables, but more difficult to simulate thousands of correlated variables. For that, you can generate a correlation matrix that has special properties, such as a Toeplitz matrix or a

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Does the US really produce the most oil now?!?

October 1, 2018
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Over the years, the US has drilled for crude oil in several locations, such as Pennsylvania, Texas, Alaska, and the Gulf of Mexico. A few years ago, as the US started drilling more in North Dakota, there were forecasts that we would surpass Saudi Arabi...
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Three of My Favorite Programming Tips

October 1, 2018
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I often get asked for programming tips. Here, I share three of my favorite tips for beginners. Tip #1: COUNTC and CATS Functions Together The CATS function concatenates all of its arguments after it strips leading and trailing blanks. The COUNTC functi...
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Chi-square tests for proportions in one-way tables

October 1, 2018
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Chi-square tests for proportions in one-way tables

Programmers on a SAS discussion forum recently asked about the chi-square test for proportions as implemented in PROC FREQ in SAS. One person asked the basic question, "how do I test the null hypothesis that the observed proportions are equal to a set of known proportions?" Another person said that

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Radial basis functions and Gaussian kernels in SAS

September 26, 2018
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Radial basis functions and Gaussian kernels in SAS

A radial basis function is a scalar function that depends on the distance to some point, called the center point, c. One popular radial basis function is the Gaussian kernel φ(x; c) = exp(-||x – c||2 / (2 σ2)), which uses the squared distance from a vector x to the

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Metacoda Auth Domain Reviewer

September 26, 2018
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One of the new Metacoda Security Plug-ins features arriving in version 6.1 is the Auth Domain Reviewer. Like the other reviewers, this plug-in is used for investigating, documenting and testing how a SAS metadata security feature has been used within a...
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River flooding in North Carolina from Hurricane Florence

September 24, 2018
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Here in North Carolina, a hurricane recently moved very slowly across our state, causing major flooding, and even closing miles of interstate highways for longer than a week. There is data available online for gauges along the river (or gages, as they ...
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How many perfect riffle shuffles are required to restore a deck to its initial order?

September 24, 2018
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How many perfect riffle shuffles are required to restore a deck to its initial order?

Last week I compared the overhand shuffle to the riffle shuffle. I used random operations to simulate both kinds of shuffles and then compared how well they mix cards. The article caused one my colleague and fellow blogger, Rob Pratt, to ask if I was familiar with a bit of

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Shuffling smackdown: Overhand shuffle versus riffle shuffle

September 19, 2018
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Shuffling smackdown: Overhand shuffle versus riffle shuffle

Every day I’m shufflin'. Shufflin', shufflin'.       -- "Party Rock Anthem," LMFAO The most popular way to mix a deck of cards is the riffle shuffle, which separates the deck into two pieces and interleaves the cards from each piece. Besides being popular with card players, the riffle shuffle is

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