Files
ioccc/1990/theorem/README.md
T
Cody Boone Ferguson 249e865de2 Mass edit README.md: remove top award/author lines
As requested on GitHub: a tool that will be written, readme2index, will,
as explained:

    '... will take the converted HTML from the README.md markdown and
    inject it into an HTML template. Things such title, award one and
    author information will be injected into the HTML page ahead of the
    HTML that was converted from the README.md markdown. Without going
    into details of HOW at this time, the result will be a coherent HTML
    index.html page with the winner title / award, winning author
    information, and important file links come from other sources and
    NOT from the README.md file.

    The text from the 1st award line, thru the authorship information,
    and up to but not including the "## To build:" line in the README.md
    file will just get in the way. Moreover authors might be tempted to
    try and maintain that top of README.md text instead of working with
    the author/_author_handle_.json and winner .winner.json files.

This was done with my[0] sgit(1) (https://github.com/xexyl/sgit) tool like:

    sgit -o -n -e '/^## To build:/,$p' '[12][0-9][0-9][0-9]/*/README.md'

[0] Is that shameless self-promotion? I don't know but I don't care: it
is generally a very useful tool and has been used in other repos too.
Besides, I've done it many times before and it's a great example that I
will be adding to the README.md file of the tool, one I hadn't thought
of doing.
2023-11-05 03:39:46 -08:00

3.3 KiB

To build:

make all

Bugs and (Mis)features:

The current status of this entry is:

STATUS: INABIAF - please **DO NOT** fix

For more detailed information see 1990 theorem in bugs.md.

To use:

./theorem expression x1 x2 h y1

where:

expression - function f(x,y)  (see below)
x1 - start of interval
x2 - end of interval
h - step size
y1 - initial value  (y(x1) == y1)

Try:

./theorem y 0 1 0.1 1

If the two args passed to fibonacci and theorem_bkp add to 0 it will print 0 over and over again in an infinite loop. In this case it should not be fixed (another condition where this occurred was fixed in 2023 as it affected usability of the program).

This is supposed to happen. As is written in the The Jargon File:

That's not a bug, that's a feature.

Judges' remarks:

The program's source implements four functions, all from the same source file!

When you compile theorem.c as is and run with 5 args, it numerically solves the equation y'=f(x,y), with a step size of h (see above usage), over the interval x=[x1,x2], with the initial condition of y(x1)=y1.

The 'expression' f(x,y) is any function of x and y with the operators:

+	-	*	/	^

The symbol ^ is the power operator. Note that it only supports integer powers. Also note that all expressions are evaluated strictly left to right. (i.e., parenthesis aren't supported).

Try running the program with the following args:

./theorem y 0 1 0.1 1
./theorem 1/x 1 2 0.1 0
./theorem 'x^2/y+x' 0 1 0.1 6

But wait, there is more! You also get, free of charge, a reversing filter! Try:

./theorem -r 0 0 0 0 < theorem.c > sorter.c

Still not impressed? The author throws in for free, a sort program! Try:

make sorter
ls | ./sorter

This program is safe for home use as well. The author has included a safety feature in case you misplace the original program source:

./sorter -r 0 0 0 0 < sorter.c > theorem_bkp.c

And finally, as a special offer to users of this entry, the author provides a Fibonacci sequence generator! Try:

./sorter 0 0 0 0 < theorem.c > fibonacci.c
make fibonacci
./fibonacci 1 1
./fibonacci 2 1

Program available on 9 track and cartridge cassette. Neither Ginsu knife nor Swiss army knife included! :-)

When this program was first shown at the 1990 Summer USENIX conference, it received a standing ovation; a first for a contest entry.

Author's remarks:

Differential equations are solved via the Runge-Kutta method, which guarantees local error proportional to h^5, and total error across a finite interval is at most a constant times h^4.

Sorting is accomplished with a standard shell sort.

Note that the sorting and reversing is limited to files with fewer than 500 lines, each less than 99 characters long.

This file is Copyright (c) 2023 by Landon Curt Noll. All Rights Reserved. You are free to share and adapt this file under the terms of this license:

Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)

For more information, see: https://creativecommons.org/licenses/by-sa/4.0/