15 July 00Bentley: FYI1 Truth, Beauty and Engineering: What I'd Like My CS Freshman Kid to Learn...

15 July 00 Bentley: FYI 1Bentley: FYI

Truth, Beauty and Engineering:What I'd Like My CS Freshman Kidto Learn Next Year

Jon BentleyBell Labs

www.programmingpearls.com/fyi.html


ContextMain Course: Curriculum Design

What content?

Which courses?

Which languages?

This Talk: Desserts and Spices

Little add-ons for first-year courses

(Weave-throughs?)


OutlineEngineering

Tricks of the Trade

Eyes Open to the World

Beauty

Elegance

Communication

Truth

History

Ethics


A QuizA TV Commercial

“U.S. college students eat 60 million slices of pizza per month.”

Is this reasonable?

How much does a one-hour lecture cost?

A program sorts one million integers in one second. How long to sort two million?

How long will an exhaustive search take to solve a TSP of size 10? 20? 30?

How much do calculus texts cost?


The Back of the EnvelopeImportant for engineers and citizens

How to teach quick calculations?

Probably not a lecture (nor even half an hour)

Woven throughout an education

What to teach

Tabular computations

Rules of thumb

Quick checks

Safety factors


Problem DefinitionFor 72 psychological subjects, randomly

permuteorder of experimenters (1, 2, 3)

stress conditions (High, Medium, Low)

Desired results 1 3L 2M 1H2 3H 1M 2L3 1L 2H 3M4 1M 2L 3H …

How to generate?


An Elegant Solution

Educational GoalsKnowledge about how to solve a problem

Wisdom about what problem to solve

123

213

132LMH

MLH

LHM


Debugging TalesA banking system “quits” on international

data.

The programmer can’t log in standing up.

A program works once twice.


Engineering Tricks of the TradeBack of the Envelope Estimates

Problem Definition

Debugging

Tradeoffs, Symmetry

Components, Prototypes

Simplicity, Elegance

programmingpearls.com/tricks.html


Engineer’s EyesHow does that CD player work?

Random play: algorithm? RNG?

How much music? Compared to MP3?

Error correction? Scratches? Bounces?

Textual description of content?

Remote control?

Store state at power off? Representation?

Navigation over a long spiral?


Real-World SoftwareYour Watch

AutomobilesEntry systems: Keys, combinations, remote

Antilock brakes, carburetors, transmissions, …

Memory for user preferences

GPS, maps, radar, HUDs, …

Count the processors! Networks?

Entry SystemsDorms, cars, arenas, turnpikes, hotel rooms, …

Sound, Pictures, Motion Pictures


Some Wonderful BooksAdams, Conceptual Blockbusting

Petroski, To Engineer Is Human

Polya, How To Solve It

Strunk and White, Elements of Style

Huff, How to Lie with Statistics

Fisher and Ury, Getting to Yes

15 July 00 Bentley: FYIBentley: FYI

OutlineEngineering

Beauty

Elegance

Communication

Truth


EleganceGordon Bell: The cheapest, fastest and most

reliable components are those that aren’t there.

Antoine de Saint Exupéry: A designer knows he has arrived at perfection not when there is no longer anything to add, but when there is no longer anything to take away.

Albert Einstein: Everything should be made as simple as possible, but no simpler.

15 July 00 Bentley: FYI

A C++ Program// count # occurrences of all characters in a file// written: 8/5/94, Owen Astrachan, modified 5/1/99

void Print(const tvector<int> & counts, int total);void Count(istream & input, tvector<int> & counts, int & total);

int main(){ int totalAlph = 0; string filename = PromptString("enter name of input file: ");

ifstream input(filename.c_str());

if (input.fail() ) { cout << "could not open file " << filename << endl; exit(1); } tvector<int> charCounts(CHAR_MAX+1,0); // all initialized to 0 Count(input,charCounts,totalAlph); Print(charCounts,totalAlph); return 0;}

void Count(istream & input, tvector<int> & counts, int & total)// precondition: input open for reading// counts[k] == 0, 0 <= k < CHAR_MAX// postcondition: counts[k] = # occurrences of character k// total = # alphabetic characters { char ch; while (input.get(ch)) // read a character { if (isalpha(ch)) // is alphabetic (a-z)? { total++; } ch = tolower(ch); // convert to lower case counts[ch]++; // count all characters } }

void Print(const tvector<int> & counts, int total)// precondition: total = total of all entries in counts['a']..counts['z']// postcondition: all values of counts from 'a' to 'z' printed { const int MIDALPH = 13; cout.setf(ios::fixed); // print 1 decimal place cout.precision(1); char k; for(k = 'a'; k <= 'm'; k++) { cout << k << setw(7) << counts[k] << " "; cout << setw(4) << 100 * double(counts[k])/total << "% \t\t"; cout << char(k+MIDALPH) << setw(7) << counts[k+MIDALPH] << " "; cout << setw(4) << 100 * double(counts[k+MIDALPH])/total << "%" << endl; }}


A Longer ProgramRoberts, The Art and Science of C (A-W, 1995)

3 1/2 pages

Functions: main, CountLetters, CountLettersInString, RecordLetter, DisplayLetterCounts, LetterIndex, ClearIntegerArray


Kernighan and Pike’s Programunsigned long count[UCHAR_MAX+1];

/* freq main: display byte frequency counts */int main(void){ int c;

while ((c = getchar()) != EOF) count[c]++;

for (c = 0; c <= UCHAR_MAX; c++) if (count[c] != 0)

printf("%.2x %c %lu\n", c, isprint(c) ? c : '-', count[c]); return 0;}


Elegant Sortsvoid isort(int *a, unsigned n){ int i, j; for (i = 1; i < n; i++) for (j = i; j > 0 && a[j-1] > a[j]; j--) swap(j, j-1, a);}

void qsort(int *a, unsigned n){ int i, j; if (n <= 1) return; for (i = 1, j = 0; i < n; i++) if (a[i] < a[0]) swap(++j, i, a); swap(0, j, a); qsort(a, j); qsort(a+j+1, n-j-1);}


Strunk and White’s Rule 17Vigorous writing is concise. A sentence

should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts. This requires not that the writer make all sentences short, or avoid all detail and treat subjects only in outline, but that every word tell.


Code in Programming PearlsSorting unique integersVector rotationAnagramsMaximum-sum subvectorBinary searchInsertion sort, quicksort, heapsortRandom samplesHeapsLongest duplicated substringsMarkov text


CommunicationEssential skill for all students

Audience: Technical and nontechnical

Writing and speaking

How to teach it?Example: Lectures, handouts, web pages, …

PracticeDocumentation

Essays

Term papers

Oral presentations


OutlineEngineering

Beauty

Truth

History

Ethics


CachingIdeally one would desire an indefinitely large

memory capacity such that any particular [word] would be immediately available.… It does not seem possible to achieve such a capacity. We are therefore forced to recognize the possibility of constructing a hierarchy of memories, each of which has greater capacity than the preceding but which is less quickly accessible.

“Preliminary discussion of the logical design of an electronic computing instrument”, Burks, Goldstine, von Neumann, 1946


Kinds of HistoryThe Field

The Human SideThe 1990 house

Organizational1965: Triangle Universities Computation Center

PersonalMy 32K computers: 1969, 1973, 1981, 1999

ArtifactsOld computers, disks

Strong’s Exhaustive Concordance


A Victorian Search EngineStrong’s Exhaustive Concordance

Sample Entrythankful See also UNTHANKFUL

Ps 100:4 be t’ unto him, and bless his name.

Ro 1:21 him not as God, neither were t’;

Col 3:15 called in one body; and be ye t’.

Compare to AltaVistahttp://gatekeeper.dec.com/pub/DEC/SRC/publications

/sites/talk/AltaVista_Technical-abs.html

A Fun Programming Exercise


History in Pearls1950’s

Brooks’s Kentucky state income tax

1960’sAnagrams; fast binary search

1970’sSuffix arrays; Maximum-sum subarray

Lesk’s touch-tone phone directory

Kernighan’s symmetric matrices

1980’sData communication within Lockheed


EthicsFirst-year Students

When may they copy text and code?Why? Vary the rules!

Social Issues: Napster? Ellison’s spies?

Older StudentsGrowing a spelling list

Snooping through files; reading mail

College privacy: prox cards, web histories, ...

Real ProblemsEthical questions that made me lose sleep


A Whole WorldCracking DVDs

How do DVDs work?Mathematics, science, technology

Back of the EnvelopeBandwidth for sharing a DVD?

History of movies and protection

Ethics

Concise Text and Code

15 July 00Bentley: FYI1 Truth, Beauty and Engineering: What I'd Like My CS Freshman Kid to Learn...

Documents

Transcript of 15 July 00Bentley: FYI1 Truth, Beauty and Engineering: What I'd Like My CS Freshman Kid to Learn...