Archive for category Engineering

Love Me I’m an Agile Scrum Master

In the 1966 song, Love Me I’m a Liberal, protest singer Phil Ochs mocked the American left for insincerely pledging support for civil rights and socialist causes. Using the voice of a liberal hypocrite, Ochs sings that he “hope[s] every colored boy becomes a star, but don’t talk about revolution; that’s going a little too far.” The refrain is, “So love me, love me, love me, I’m a liberal.” Putting Ochs in historical context, he hoped to be part of a major revolution and his anarchic expectations were deflated by moderate democrats. In Ochs’ view, limousine liberals and hippies with capitalist leanings were eroding the conceptual purity of the movement he embraced.

If Ochs were alive today, he probably wouldn’t write software; but if he did he’d feel right at home in faux-agile development situations where time-boxing is a euphemism for scheduling, the scrum master is a Project Manager who calls Agile a process, and a goal has been set for increased iteration velocity and higher story points per cycle. Agile can look a lot like the pre-Agile world these days. Scrum in the hands of an Agile imposter who interprets “incremental” to mean “sequential” makes an Agile software project look like a waterfall.

While it’s tempting to blame the abuse and dilution of Agile on half-converts who endorsed it insincerely – like Phil Ochs’ milquetoast liberals – we might also look for cracks in the foundations of Agile and Scrum (Agile is a set of principles, Scrum is a methodology based on them). After all, is it really fair to demand conformity to the rules of a philosophy that embraces adaptiveness? Specifically, I refer to item 4 in the list of values called out in the Agile Manifesto:

  1. Individuals and interactions over processes and tools
  2. Working software over comprehensive documentation
  3. Customer collaboration over contract negotiation
  4. Responding to change over following a plan

A better charge against those we think have misapplied Agile might be based on consistency and internal coherence. That is, item 1 logically puts some constraints on item 4. Adapting to a business situation by deciding to value process and tools over individuals can easily be said to violate the spirit of the values. As obvious as that seems, I’ve seen a lot of schedule-driven “Agile teams” bound to rigid, arbitrary coding standards imposed by a siloed QA person, struggling against the current toward a product concept that has never been near a customer. Steve Jobs showed that a successful Product Owner can sometimes insulate himself from real customers; but I doubt that approach is a good bet on average.

It’s probably also fair to call foul on those who “do Agile” without self-organizing teams and without pushing decision-making power down through an organization. Likewise, the manifesto tells us to build projects around highly motivated individuals and give them the environment and trust they need to get the job done. This means we need motivated developers worthy of trust who actually can the job done, i.e., first rate developers. Scrum is based on the notion of a highly qualified self-organizing, self-directed development team. But it’s often used by managers as an attempt to employ, organize, coordinate and direct an under-qualified team. Belief that Scrum can manage and make productive a low-skilled team is widespread. This isn’t the fault of Scrum or Agile but just the current marker of the enduring impulse to buy software developers by the pound.

But another side of this issue might yet point to a basic flaw in Agile. Excellent developers are hard to find. And with a team of excellent developers, any other methodology would work as well. Less competent and less experienced workers might find comfort in rules, thereby having little motivation or ability to respond to change (Agile value no. 4).

As a minor issues with Agile/Scrum, some of the terminology is unfortunate. Backlog traditionally has a negative connotation. Starting a project with backlog on day one might demotivate some. Sprint surely sounds a lot like pressure is being applied; no wonder backsliding scrum masters use it to schedule. Is Sprint a euphemism for death-march? And of all the sports imagery available, the rugby scrum seems inconsistent with Scrum methodology and Agile values. Would Scrum Servant change anything?

The idea of using a Scrum burn-down chart to “plan” (euphemism for schedule) might warrant a second look too. Scheduling by extrapolation may remove the stress from the scheduling activity; but it’s still highly inductive and the future rarely resembles the past. The final steps always take the longest; and guessing how much longer than average is called “estimating.” Can we reconcile any of this with Agile’s focus on being value-driven, not plan-driven? Project planning, after all, is one of the erroneous assumptions of software project management that gave rise to Agile.

Finally, I see a disconnect between the method of Scrum and the values of Agile. Scrum creates a perverse incentive for developers to continually define sprints that show smaller and smaller bits of functionality. Then a series of highly successful sprints, each yielding a workable product, only asymptotically approaches the Product Owner’s goal.

Are Agile’s days numbered, or is it a good mare needing a better jockey?

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“People who enjoy meetings should not be in charge of anything.” – Thomas Sowell

 

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Marcus Vitruvius’s Science

Science, as an enterprise that acquires knowledge and justified beliefs in the form of testable predictions by systematic iterations of observation and math-based theory, started around the 17th century, somewhere between Copernicus and Newton. That, we learned in school, was the beginning of the scientific revolution. Historians of science tend to regard this great revolution as the one that never happened. That is, as Floris Cohen puts it, the scientific revolution, once an innovative and inspiring concept, has since turned into a straight-jacket. Picking this revolution’s starting point, identifying any cause for it, and deciding what concepts and technological innovations belong to it are problematic.

That said, several writers have made good cases for why the pace of evolution – if not revolution – of modern science accelerated dramatically  in Europe, only when it did, why it has continuously gained steam rather than petering out, its primary driving force, and the associated transformations in our view of how nature works. Some thought the protestant ethic and capitalism set the stage for science. Others thought science couldn’t emerge until the alliance between Christianity and Aristotelianism was dissolved. Moveable type and mass production of books can certainly claim a role, but was it really a prerequisite? Some think a critical mass of ancient Greek writings had to have been transferred to western Europe by the Muslims. The humanist literary critics that enabled repair and reconstruction of ancient texts mangled in translation from Greek to Syriac to Persian to Latin and botched by illiterate medieval scribes certainly played a part. If this sounds like a stretch, note that those critics seem to mark the first occurrence of a collective effort by a group spread across a large geographic space using shared standards to reach a peer-reviewed consensus – a process sharing much with modern science.

But those reasons given for the scientific revolution all have the feel of post hoc theorizing. Might intellectuals of the day, observing these events, have concluded that a resultant scientific revolution was on the horizon? Francis Bacon comes closest to fitting this bill, but his predictions gave little sense that he was envisioning anything like what really happened.

I’ve wondered why the burst of progress in science – as differentiated from plain know-how, nature-knowledge, art, craft, technique, or engineering knowledge – didn’t happen earlier. Why not just after the period of innovation in from about 1100 to 1300 CE in Europe. In this period Jean Buridan invented calculators and almost got the concept of inertia right. Robert Grosseteste hinted at the experiment-theory model of science. Nicole Oresme debunked astrology and gave arguments for a moving earth. But he was the end of this line. After this brief awakening, which also included the invention of banking and the university, progress came to a screeching halt. Some blame the plague, but that can’t be the culprit. Literature of the time barley mentions the plague. Despite the death toll, politics and war went on as usual; but interest in resurrecting ancient Greek knowledge of all sorts tanked.

Why not in the Islamic world in the time of Ali al-Qushji and al-Birjandi? Certainly the mental capacity was there. A layman would have a hard time distinguishing al-Birjandi’s arguments and thought experiments for the earth’s rotation from those of Galileo. But Islamic civilization at the time had plenty of scholars but no institutions for making practical use of such knowledge and its society would not have tolerated displacement of received wisdom by man-made knowledge.

The most compelling case for civilization having been on the brink of science at an earlier time seems to be the late republic or early imperial Rome. This may seem a stretch, since Rome is much more known for brute force than for finesse, despite their flying buttresses, cranes, fire engines, central heating and indoor plumbing.

Consider the writings of one Vitruvius, likely Marcus Vitruvius Pollio, in the early reign of Augustus. Vitruvius wrote De Architectura, a ten volume guide to Roman engineering knowledge. Architecture, in Latin, translates accurately into what we call engineering. Rediscovered and widely published during the European renaissance as a standard text for engineers, Vitruvius’s work contains text that seems to contradict what we were all taught about the emergence of the – or a  – scientific method.

Vitruvius is full of surprises. He acknowledges that he is not a scientist (an anachronistic but fitting term) but a collator of Greek learning from several preceding centuries. He describes vanishing point perspective: “…the method of sketching a front with the sides withdrawing into the background, the lines all meeting in the center of a circle.” (See photo below of a fresco in the Oecus at Villa Poppea, Oplontis showing construction lines for vanishing point perspective.) He covers acoustic considerations for theater design, explains central heating technology, and the Archimedian water screw used to drain mines. He mentions a steam engine, likely that later described by Hero of Alexandria (aeolipile drawing at right), which turns heat into rotational energy. He describes a heliocentric model passed down from ancient Greeks. To be sure, there is also much that Vitruvius gets wrong about physics. But so does Galileo.

Most of De Architectura is not really science; it could more accurately be called know-how, technology, or engineering knowledge. Yet it’s close. Vitruvius explains the difference between mere machines, which let men do work, and engines, which derive from ingenuity and allow storing energy.

What convinces me most that Vitruvius – and he surely could not have been alone – truly had the concept of modern scientific method within his grasp is his understanding that a combination of mathematical proof (“demonstration” in his terms) plus theory, plus hands-on practice are needed for real engineering knowledge. Thus he says that what we call science –  theory plus math (demonstration) plus observation (practice) –  is essential to good engineering.

The engineer should be equipped with knowledge of many branches of study and varied kinds of learning, for it is by his judgement that all work done by the other arts is put to test. This knowledge is the child of practice and theory. Practice is the continuous and regular exercise of employment where manual work is done with any necessary material according to the design of a drawing. Theory, on the other hand, is the ability to demonstrate and explain the productions of dexterity on the principles of proportion.

 It follows, therefore, that engineers who have aimed at acquiring manual skill without scholarship have never been able to reach a position of authority to correspond to their pains, while those who relied only upon theories and scholarship were obviously hunting the shadow, not the substance. But those who have a thorough knowledge of both, like men armed at all points, have the sooner attained their object and carried authority with them.

 It appears, then, that one who professes himself an engineer should be well versed in both directions. He ought, therefore, to be both naturally gifted and amenable to instruction. Neither natural ability without instruction nor instruction without natural ability can make the perfect artist. Let him be educated, skillful with the pencil, instructed in geometry, know much history, have followed the philosophers with attention, understand music, have some knowledge of medicine, know the opinions of the jurists, and be acquainted with astronomy and the theory of the heavens. – Vitruvius – De Architectura, Book 1

Historians, please correct me if you know otherwise, but I don’t think there’s anything else remotely like this on record before Isaac Newton – anything in writing that comes this close to an understanding of modern scientific method.

So what went wrong in Rome? Many blame Christianity for the demise of knowledge in Rome, but that is not the case here. We can’t know for sure, but the later failure of science in the Islamic world seems to provide a clue. Society simply wasn’t ready. Vitruvius and his ilk may have been ready for science, but after nearly a century of civil war (starting with the Italian social wars), Augustus, the senate, and likely the plebes, had seen too much social innovation that all went bad. The vision of science, so evident during the European Enlightenment, as the primary driver of social change, may have been apparent to influential Romans as well, at a time when social change had lost its luster. As seen in writings of Cicero and the correspondence between Pliny and Trajan, Rome now regarded social innovation with suspicion if not contempt. Roman society, at least its government and aristocracy, simply couldn’t risk the main byproduct of science – progress.

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History is not merely what happened: it is what happened in the context of what might have happened. – Hugh Trevor-Roper – Oxford Valedictorian Address, 1998

The affairs of the Empire of letters are in a situation in which they never were and never will be again; we are passing now from an old world into the new world, and we are working seriously on the first foundation of the sciences. – Robert Desgabets, Oeuvres complètes de Malebranche, 1676

Newton interjected historical remarks which were neither accurate nor fair. These historical lapses are a reminder that history requires every bit as much attention to detail as does science – and the history of science perhaps twice as much. – Carl Benjamin Boyer, The Rainbow: From Myth to Mathematics, 1957

Text and photos  © 2015 William Storage

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Pure Green Sense

With some sadness I recently received a Notice of Assignment for the Benefit of Creditors signaling the demise of PureSense Environmental, Inc. PureSense was real green – not green paint.

It’s ironic that PureSense was so little known. Environmental charlatans and quacks continue to get venture capital and government grants for businesses built around absurd “green” products debunkable by anyone with knowledge of high school physics. PureSense was nothing like that. Their down-to-earth (literally) concept provides real-time irrigation and agricultural field management with inexpensive hardware and sophisticated software. Their matrix of sensors record soil moisture, salinity, soil temperature and climate data from crop fields every 15 minutes. Doing this eliminates guesswork, optimizing use of electricity, water, and pesticides. Avoiding over- and under-watering maximizes crop yield while minimizing use of resources. It’s a win-win.

But innovation and farming are strange bedfellows. Apparently, farmers didn’t all jump at the opportunity. I did some crop disease modelling work for PureSense a few years back. Their employees told me that a common response to showing farmers that their neighbors had substantially increased yield using PureSense was along the lines of, “we’re doing ok with what we’ve got…” Perhaps we shouldn’t be surprised. Not too long ago, farmers who experimented too wildly left no progeny.

The ever fascinating Jethro Tull, inventor of the modern seed drill and many other revolutionary farming gadgets in the early 1700s, was flabbergasted at the reluctance of farmers to adopt his tools and methods. Tull wrote on Soil and Civilization, predicting that future people would have easier lives, since “the Produce of Land Will be Increased, and the Usual Expence Lessened” through a scientific (though that word is an anachronism) approach to agriculture.

The editor of his 2nd edition of his Horse-hoeing Husbandry, Or, An Essay on the Principles of Vegetation and Tillage echoed Tull’s astonishment at farmers’ behavior.

 How it has happened that a Method of Culture which proposes such advantages to those who shall duly prosecute it, hath been so long neglected in this Country, may be matter of Surprize to such as are not acquainted with the Characters of the Men on whom the Practice thereof depends; but to those who know them thoroughly it can be done. For it is certain that very few of them can be prevailed on to alter their usual Methods upon any consideration; though they are convinced that their continuing therein disables them from paying their Rents, and maintaining their Families.

 And, what is still more to be lamented, these People are so much attached to their old Customs, that they are not only averse to alter them themselves, but are moreover industrious to prevent others from succeeding, who attempt to introduce anything new; and indeed have it too generally in their Power, to defeat any Scheme which is not agreeable to their own Notions; seeing it must be executed by the same sort of Hands.

Tull could have predicted PureSense’s demise. I think its employees could have as well. GlassDoor comments suggested that PureSense needed “a more devoted sales staff.” That is likely an understatement given the market. A more creative sales model might be more on the mark. Knowing that farmers, even while wincing at ever-shrinking margins, will cling to their established methods for better or worse, PureSense should perhaps have gotten closer to the culture of farming.

PureSense’s possible failure to tap into farmers’ psyche aside, America’s vulnerability to futuristic technobabble is no doubt a major funding hurdle. You’d think that USDA REAP loan providers  and NRCS Conservation Innovation Grants programs would be lining up at their door. But I suspect crop efficiency pales in wow factor compared to a cylindrical tower of solar cells that somehow magically increases the area of sun-facing photovoltaics (hint: Solyndra’s actual efficiency was about 8.5%, a far cry from their claims that got them half a billion from the Obama administration).

Ozzie Zehner nailed this problem in Green Illusions. In his chapter on the alternative-energy fetish, he discusses energy pornographers, the enviro-techno-enthusiasts who jump to spend billions on dubious green tech that yields less benefit than home insulation and proper tire inflation would. Insulation, light rail, and LED lighting isn’t sexy; biofuels, advanced solar, and stratospheric wind turbines are. Jethro Tull would not have been surprised that modern farmers are as resistant to change as those of 17th century Berkshire. But I think he’d be appalled to learn the extent to which modern tech press, business and government line up for physics-defying snake oil while ignoring something as fundamental as agriculture.

As I finished writing this I learned that Jain Irrigation has just acquired the assets of PureSense and has pledged a long-term commitment to the PureSense platform.

Jethro Tull smiles.

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More Philosophy for Engineers

In a post on Richard Feynman and philosophy of science, I suggested that engineers would benefit from a class in philosophy of science. A student recently asked if I meant to say that a course in philosophy would make engineers better at engineering – or better philosophers. Better engineers, I said.

Here’s an example from my recent work as an engineer  that drives the point home.

I was reviewing an FMEA (Failure Mode Effects Analysis) prepared by a high-priced consultancy and encountered many cases where a critical failure mode had been deemed highly improbable on the basis that the FMEA was for a mature system with no known failures.

How many hours of operation has this system actually seen, I asked. The response indicated about 10 thousand hours total.

I said on that basis we could assume a failure rate of about one per 10,001 hours. The direct cost of the failure was about $1.5 million. Thus the “expected value” (or “mathematical expectation” – the probabilistic cost of the loss) of this failure mode in a 160 hour mission is $24,000 or about $300,000 per year (excluding any secondary effects such as damaged reputation). With that number in mind, I asked the client if they wanted to consider further mitigation by adding monitoring circuitry.

I was challenged on the failure rate I used. It was, after all, a mature, ten year old system with no recorded failures of this type.

Here’s where the analytic philosophy course those consultants never took would have been useful.

You simply cannot justify calling a failure mode extremely rare based on evidence that it is at least somewhat rare. All unique events – like the massive rotor failure that took out all three hydraulic systems of a DC-10 in Sioux City – were very rare before they happened.

The authors of the FMEA I was reviewing were using unjustifiable inductive reasoning. Philosopher David Hume debugged this thoroughly in his 1738 A Treatise of Human Nature.

Hume concluded that there simply is no rational or deductive basis for  induction, the belief that the future will be like the past.

Hume understood that, despite the lack of justification for induction, betting against the sun rising tomorrow was not a good strategy either. But this is a matter of pragmatism, not of rationality. A bet against the sunrise would mean getting behind counter-induction; and there’s no rational justification for that either.

In the case of the failure mode not yet observed, however, there is ample justification for counter-induction. All mechanical parts and all human operations necessarily have nonzero failure or error rates. In the world of failure modeling, the knowledge “known pretty good” does not support the proposition “probably extremely good”, no matter how natural the step between them feels.

Hume’s problem of induction, despite the efforts of Immanuel Kant and the McKinsey consulting firm, has not been solved.

A fabulously entertaining – in my view – expression of the problem of induction was given by philosopher Carl Hempel in 1965.

Hempel observed that we tend to take each new observation of a black crow as incrementally supporting the inductive conclusion that all crows are black. Deductive logic tells us that if a conditional statement is true, its contrapositive is also true, since the statement and its contrapositive are logically equivalent. Thus if all crows are black then all non-black things are non-crow.

It then follows that if each observation of black crows is evidence that all crows are black (compare: each observation of no failure is evidence that no failure will occur), then each observation of a non-black non-crow is also evidence that all crows are black.

Following this line, my red shirt is confirming evidence for the proposition that all crows are black. It’s a hard argument to oppose, but it simply does not “feel” right to most people.

Many try to salvage the situation by suggesting that observing that my shirt is red is in fact evidence that all crows are black, but provides only unimaginably small support to that proposition.

But pushing the thing just a bit further destroys even this attempt at rescuing induction from the clutches of analysis.

If my red shirt gives a tiny bit of evidence that all crows are black, it then also gives equal support to the proposition that all crows are white. After all, my red shirt is a non-white non-crow.

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Incommensurability and the Design-Engineering Gap

Those who conceptualize products – particularly software – often have the unpleasant task of explaining their conceptual gems to unimaginative, sanctimonious engineers entrenched in the analytic mire of in-the-box thinking. This communication directs the engineers to do some plumbing and flip a few switches that get the concept to its intended audience or market… Or, at least, this is how many engineers think they are viewed by designers.
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Truth is, engineers and creative designers really don’t speak the same language. This is more than just a joke. Many posts here involve philosopher of science, Thomas Kuhn. Kuhn’s idea of incommensurability between scientific paradigms also fits the design-engineering gap well. Those who claim the label, designers, believe design to be a highly creative, open-ended process with no right answer. Many engineers, conversely, understand design – at least within their discipline – to mean a systematic selection of components progressively integrated into an overall system, guided by business constraints and the laws of nature and reason. Disagreement on the meaning of design is just the start of the conflict.

Kuhn concluded that the lexicon of a discipline constrains the problem space and conceptual universe of that discipline. I.e., there is no fundamental theory of meaning that applies across paradigms. The meaning of expressions inside a paradigm comply only with the rules of that paradigm.  Says Kuhn, “Conceptually, the world is our representation of our niche, the residence of the particular human community with whose members we are currently interacting” (The Road Since Structure, 1993, p. 103). Kuhn was criticized for exaggerating the extent to which a community’s vocabulary and word usage constrains the thoughts they are able to think. Kuhn saw this condition as self-perpetuating, since the discipline’s constrained thoughts then eliminate any need for expansion of its lexicon. Kuhn may have overplayed his hand on incommensurability, but you wouldn’t know it from some software-project kickoff meetings I’ve attended.

This short sketch, The Expert, written and directed by Lauris Beinerts, portrays design-engineering incommensurability from the perspective of the sole engineer in a preliminary design meeting.

See also: Debbie Downer Doesn’t Do Design

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Sun Follows the Solar Car

Bill Storage once got an A in high school Physics and suggests no further credentials are needed to evaluate the claims of most eco-fraud.

Once a great debate raged in America over the matter of whether man-mad climate change had occurred. Most Americans believed that it had. There were theories, models, government-sponsored studies, and various factions arguing with religious fervor. The time was 1880 and the subject was whether rain followed the plow – whether the westward expansion of American settlers beyond the 100th meridian had caused an increase in rain that would make agricultural life possible in the west. When the relentless droughts of the 1890s offered conflicting evidence, the belief died off, leavings its adherents embarrassed for having taken part in a mass delusion.

Model TWe now know the dramatic greening of the west from 1845 to 1880 was due to weather, not climate. It was not brought on by Mormon settlements, vigorous tilling, or the vast amounts of dynamite blown off to raise dust around which clouds could form. There was a shred of scientific basis for the belief; but the scale was way off.

It seems that the shred of science was not really a key component of the widespread belief that rain would follow the plow. More important was human myth-making and the madness of crowds. People got swept up in it. As ancient Jewish and Roman writings show, public optimism and pessimism ebbs and flows across decades. People confuse the relationship between man and nature. They either take undue blame or undo credit for processes beyond their influence, or they assign their blunders to implacable cosmic forces. The period of the Western Movement was buoyant, across political views and religions. Some modern writers force-fit the widely held belief about rain following the plow in the 1870s into the doctrine of Manifest Destiny. These embarrassing beliefs were in harmony, but were not tied genetically. In other words, don’t blame the myth that rain followed the plow on the Christian right.

Looking back, one wonders how farmers, investors and politicians, possibly including Abraham Lincoln, could so deeply indulge in belief held on irrational grounds rather than evidence and science. Do modern humans do the same? I’ll vote yes.

Today’s anthropogenic climate theories have a great deal more scientific basis than those of the 1870s. But many of our efforts at climate cure do not. Blame shameless greed for some of the greenwashing; but corporations wouldn’t waste their time if consumers weren’t willing to waste their dollars and hopes.

Take Ford’s solar-powered hybrid car, about which a SmartPlanet writer recently said:

Imagine an electric car that can charge without being plugged into an outlet and without using electricity from dirty energy sources, like coal.

He goes on to report that Ford plans to experiment with such a solar-hybrid concept car having a 620-mile range. I suspect many readers will understand that experimentation to mean experimenting in the science sense rather than in the marketability sense. Likewise I’m guessing many readers will allow themselves to believe that such a car might derive a significant part of the energy used in a 620-mile run from solar cells.

We can be 100% sure that Ford is not now experimenting on – nor will ever experiment on – a solar-powered car that will get a significant portion of its energy from solar cells. It’s impossible now, and always will be. No technology breakthrough can alter the laws of nature. Only so much solar energy hits the top of a car. Even if you collected every photon of it, which is again impossible because of other laws of physics, you couldn’t drive a car very far on it.

Most people – I’d guess – learned as much in high school science. Those who didn’t might ask themselves, based on common sense and perhaps seeing the size of solar panels needed to power a telephone in the desert, if a solar car seems reasonable.

The EPA reports that all-electric cars like the Leaf and Tesla S get about 3 miles per kilowatt-hour of energy. The top of a car is about 25 square feet. At noon on June 21st in Phoenix, a hypothetically perfect, spotless car-top solar panel could in theory generate 30 watts per square foot.  You could therefore power half of a standard 1500 watt toaster with that car-top solar panel. If you drove your car in the summer desert sun for 6 hours and the noon sun magically followed it into the shade and into your garage – like rain following the plow – you could accumulate 4500 watt-hours (4.5 kilowatt hours) of energy, on which you could drive 13.5 miles, using the EPA’s numbers. But experience shows that 30 watts per square foot is ridiculously optimistic. Germany’s famous solar parks, for example, average less than one watt per square foot; their output is a few percent of my perpetual-noon-Arizona example. Where you live, it probably doesn’t stay noon, and you’re likely somewhat north of Phoenix, where the sun is far closer to the horizon, and it’s not June 21st all year (hint: sine of 35 degrees times x, assuming it’s not dark). Oh, and then there’s clouds. If you live in Bavaria or Cleveland, or if your car roof’s dirty – well, your mileage may vary.

Recall that this rather dim picture cannot be made much brighter by technology. Physical limits restrict the size of the car-top solar panel, nature limits the amount of sun that hits it, and the Shockley–Queisser limit caps the conversion efficiency of solar cells.

Curbing CO2 emissions is not a lost cause. We can apply real engineering to the problem. Solar panels on cars isn’t real engineering; it’s pandering to public belief. What would Henry Ford think?

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Tom Hight is my name, an old bachelor I am,
You’ll find me out West in the country of fame,
You’ll find me out West on an elegant plain,
And starving to death on my government claim.

Hurrah for Greer County!
The land of the free,
The land of the bed-bug,
Grass-hopper and flea;
I’ll sing of its praises
And tell of its fame,
While starving to death
On my government claim.

Opening lyrics to a folk song by Daniel Kelley, late 1800s

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Is Fault Tree Analysis Deductive?

Endeavor over Golden Gate BridgeAn odd myth persists in systems engineering and risk analysis circles. Fault tree analysis (FTA), and sometimes fault trees themselves, are said to be deductive. FMEAs are called inductive. How can this be?

By fault trees I mean Boolean logic modeling of unwanted system states by logical decomposition of equipment fault states into combinations of failure states of more basic components. You can read more on fault tree analysis and its deductive nature at Wikipedia. By FMEA (Failure Mode & Effects Analysis) I mean recording all the things that can go wrong with the components of a system. Writers who find fault trees deductive also find FMEAs, their complement, to be inductive. I’ll argue here that building fault trees is not a deductive process, and that there is possible harm in saying so. Secondarily, I’ll offer that while FMEA creation involves inductive reasoning, the point carries little weight, since the rest of engineering is inductive reasoning too.

Word meanings can vary with context; but use of the term deductive is consistent across math, science, law, and philosophy. Deduction is the process of drawing a logically certain conclusion about a particular instance from a rule or premise about the general. Assuming all men are mortal, if Socrates is a man, then he is mortal. This is true regardless of the meaning of the word mortal. It’s truth is certain, even if Socrates never existed, and even if you take mortal to mean living forever.

Example from a software development website:

FMECA is an inductive analysis of system failure, starting with the presumed failure of a component and analyzing its effect on system stability: “What will happen if valve A sticks open?” In contrast, FTA is a deductive analysis, starting with potential or actual failures and deducing what might have caused them: “What could cause a deadlock in the application?”

The well-intended writer says we deduce the causes of the effects in question. Deduction is not up to that task. When we infer causes from observed effects, we are using induction, not deduction.

How did the odd claims that fault trees and FTAs are deductive arise? It might trace to William Vesely, NASA’s original fault tree proponent. Vesely sometimes used the term deductive in his introductions to fault trees. If he meant that the process of reducing fault trees into cut sets (sets of basic events or initiators) is deductive, he was obviously correct. But calculation isn’t the critical aspect of fault trees; constructing them is where the effort and need for diligence lie. Fault tree software does the math. If Vesely saw the critical process of constructing fault trees and supplying them with numerical data (often arduous, regardless of software) as deductive – which I doubt – he was certainly wrong. 

Inductive reasoning, as used in science, logic and philosophy, means inferring general rules or laws from observations of particular instances. The special use of the term math induction actually refers to deduction, as mathematicians are well aware. Math induction is deductive reasoning with a confusing title. Induction in science and engineering stems from our need to predict future events. We form theories about how things will behave in the future based on observations of how similar things behaved in the past. As I discussed regarding Bacon vs. Descartes, science is forced into the realm of induction because deduction never makes contact with the physical world – it lives in the mind.

Inductive reasoning is exactly what goes on when you construct a fault tree. You are making inferences about future conditions based on modeling and historical data – a purely inductive process. The fact that you use math to solve fault trees does not make fault trees any more deductive than the presence of math in lab experiments makes empirical science deductive.

Does this matter?

It’s easy enough to fix this technical point in descriptions fault tree analysis. We should do so, if merely to avoid confusing students. But more importantly, quantitative risk analysis – including FTA – has its enemies. They range from several top consultancies selling subjective, risk-score matrix methodologies dressed up in fancy clothes (see Tony Cox’s SIRA presentation on this topic) to some of NASA’s top management – those flogged by Richard Feynman in his minority report on the Challenger disaster. The various criticisms of fault tree analysis say it is too analytical and correlates poorly with the real world. Sound familiar? It echoes a feud between the heirs of Bacon (induction) and the heirs of Descartes (deduction). Some of fault trees’ foes find them overly deductive. They then imply that errors found in past quantitative analyses impugn objectivity itself, preferring subjective analyses based on expert opinion. This curious conclusion would not follow, even if fault tree analyses were deductive, which they are not.

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Science is the belief in the ignorance of experts. – Richard Feynman

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