Add pml article on installing RGtk2 toolkit on OSX

markdown/pml-installingRattleOnMacOSX.md

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+## Installing Rattle on Macbook OSX
+
+The `rattle` package is referenced during the *Practical Machine Learning* course in the Johns Hopkins Data Science Specialization as a mechanism to print nice looking tree diagrams from the model output generated by the `rpart` package. Unfortunately, the package has a dependency on the `gtk2` library that is not present by default on Mac OSX.
+
+Therefore, students using OSX frequently post questions about how to install the components necessary to use the Rattle `fancyRpartPlot()` function.
+
+After a fair amount of effort I was able to install rattle on Mac OS X Sierra.
+
+The install requires the gtk toolkit, and on Mac one must do the following, per a solution on [stackoverflow.com](https://stackoverflow.com/questions/15868860/r-3-0-and-gtk-rgtk2-error).  
+
+1. [Install macports](https://www.macports.org/install.php) — tool for installing mac packages <br><br>
+2. run SUDO to install gtk2 on mac<br> `sudo port install gtk2  ## (X11 -- not aqua)`<br><br>
+3. export new path <br>`export PATH=/opt/local/bin:/opt/local/sbin:$PATH`<br><br>
+4. From RStudio, install rgtk2 with<br> `install.packages(“RGtk2”)` including compile<br><br>
+
+The most complete set of instructions is located at [Sebastian Kopf's Gist page](https://gist.github.com/sebkopf/9405675) and verified by my own install on June 17, 2017. Once installed, loading the rattle library will generate the following output in the R console.
+
+<img src="./images/pml-installingRattleOnMacOSX01.png">
+
+In order to use `fancyRpartPlot()`, students will also need to install the `rpart.plot` package.
+
+      install.packages("rpart.plot")
+
+## Example: Fancy Rpart Plot of Iris Data
+
+Here we've replicated the code needed to generate a fancy tree diagram with `caret` and `rattle` that is discussed in the *Practical Machine Learning* lecture on *Predicting with Trees*.
+
+      library(caret)
+      library(rattle)
+      inTrain <- createDataPartition(y = iris$Species,
+                                     p = 0.7,
+                                     list = FALSE)
+      training <- iris[inTrain,]
+      testing <- iris[-inTrain,]
+      modFit <- train(Species ~ .,method = "rpart",data = training)
+      fancyRpartPlot(modFit$finalModel)
+
+<img src="./images/pml-installingRattleOnMacOSX02.png">

statinf-integralCalculations.Rmd

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+---
+title: "statinf-integralCalculations"
+author: "Len Greski"
+date: "8/5/2017"
+output: html_document
+---
+
+```{r setup, include=FALSE}
+knitr::opts_chunk$set(echo = TRUE)
+```
+
+## Fixed Integral of a Point
+
+$\int_{a}^{a} f(x) dx = 0$
+
+## Standard Deviation from Census Table Data
+
+$s = \frac{x_{5 ptile}-\bar{x}}{Z_{5 ptile}}$.