Environmental Decisions in the Face of Uncertainty

New report from the National Academies Press on decision making under uncertainty.

Description: The U.S. Environmental Protection Agency (EPA) is one of several federal agencies responsible for protecting Americans against significant risks to human health and the environment. As part of that mission, EPA estimates the nature, magnitude, and likelihood of risks to human health and the environment; identifies the potential regulatory actions that will mitigate those risks and protect public health1 and the environment; and uses that information to decide on appropriate regulatory action. Uncertainties, both qualitative and quantitative, in the data and analyses on which these decisions are based enter into the process at each step. As a result, the informed identification and use of the uncertainties inherent in the process is an essential feature of environmental decision making.

No Interactions? OFAT is still a Bad Idea

PDF version

Suppose you are trying to estimate the effect that 6 factors have on a response, and you know that none of the factors influence the effect of the others, so that a simple model like this

$$Y=b_1{X}_1+b_2{X}_2+b_3{X}_3+b_4{X}_4+b_5{X}_5+b_6{X}_6$$

(1)

is the perfect choice. How should you get the data you need to estimate the $b_i$’s? You may be tempted to design a test to estimate each of these factors by changing one factor at a time (OFAT). There are no interaction terms (e.g. $b_7{X}_1{X}_4$) in equation 1. So there’s no need to perform any runs that change several of the $X$’s at once, right? Wrong.

Octet Truss Memory, Time and Dollar Costs

Cost for 3D Octet Truss Arrays

	i	j	k	time (s)	stl (bytes)	WSF ($)
1	1	1	1	1.47	73384
2	2	2	2	28.74	435384	2.61
3	3	3	3	173.32	1342184	4.99
4	4	4	4	873.20	3052984	9.46
5	5	5	5	2952.67	5826984	16.69
6	6	6	6	6694.16	9923484	27.32

This is a follow-up to the previous post on using the octet truss for topology optimization. The memory cost of performing the union of all the truss members in BRLCAD to generate stl files for printing was too large for the ToPy dogleg example so I generated a set of stl files for a range of arrays of octet truss unit cells. Then I uploaded them to shapeways to see how much they would cost to print in the white-strong-flexible nylon material. The table shows how long the python script took to execute, the size of the resulting stl file, and the cost to print the part on Shapeways in the white-strong-flexible material.

Small Multiple Scatter Plots with Marginal Densities

An example data visualization in R inspired by Tufte's example on pp118-121 of Beautiful Evidence; source below the fold.

HIFiRE-5 Flight Test Preliminary Results and Video

Check out the preliminary results on AIAA's ARC site: HIFiRE-5 Flight Test Preliminary Results

Maxima Related Lisp Tutorials

In this previous post I mentioned that I learn a lot from the Maxima mailing list.

There was a recent question (somewhat frequently asked) about how to learn Lisp to be a better Maxima user / developer that is a great example of that. The thread is called Lisp tutorial. The original poster has a simple request:

Hi,
I have enjoyed using Maxima to solve differential equations. I would like
to learn lisp to complement Maxima. Can any of the maintainers of Maxima
(or others for that matter) recommend a lisp tutorial?
Many thanks

Ronald F. Modesitt

The list responded with a variety of resources.

• The Common Lisp wiki: Getting Started.
  
• Practical Common Lisp
  
• Paradigms of Artificial Intelligence Programming: Case Studies in Common Lisp (on Amazon), companion site by Norvig
  
• Common Lisp: A Gentle Introduction to Symbolic Computation by Turetsky has also been previously mentioned on the list
  

Norvig's PAIP (which I was quite happy to get as a present over the holidays) is especially relevant to Maxima users. Chapter 8, Symbolic Mathematics: A Simplification Program, has a simple symbolic algebra implementation, and Chapter 15, Symbolic Mathematics with Canonical Form, has a more capable solution. Both chapters are modeled on Maxima.

Nuclear Rockets Petition

As reported by NBC there is a petition on WhiteHouse.gov to rapidly develop and deploy a nuclear thermal rocket for both manned & un-manned space missions. I signed it; why not? Here's the short url: http://wh.gov/UVuD

Nuclear rocketry seems to be a popular topic of late. Gary Johnson has a recent post about nuclear rockets. The NBC article mentions NERVA. There is also the more recent Project Timberwind and Space Nuclear Thermal Propulsion program effort to develop nuclear upper-stages.

Scientific Computing Going Mobile/Embedded

I follow both the Octave and Maxima user mailing lists (I learn more from the Maxima list, but the Octave one still throws up a gem every now and then). I am also a founding member of the Dayton Diode hackerspace. So it was interesting to see some things of interest to makers/hackers pop-up on those two lists.

The first was a thread on the Octave list about installing Octave and the Octave Forge packages on a Raspberry Pi. In theory it should be as easy as any other Debian system using the package manager for the distribution. No word back from the OP yet on whether it works in practice or not.

The second thread to pop up was on the Maxima list about installing Maxima on Android systems. Maxima-on-Android is apparently a bundle on Google Play of Maxima 5.28.0, Gnuplot 4.6, Mathjax 2.1 and Qepcad 1.69. I have not played with it yet on any of my Android devices.

National Strategy for Advancing Climate Modeling

NAP has a new report out on a national strategy for advancing climate modeling. I've just done a quick skim so far. Some tidbits below that touch on V&V and uncertainty.