Best of Show
Adrian Mariano University of Washington 2729 72nd Ave SE Mercer Island, WA 98040 USA
To build:
make all
Cody Boone Ferguson fixed some bugs that
impacted the usability of this program including some segfaults under modern
systems (and possibly in some cases earlier systems) with this entry.
Originally we noted that the 4 trailing args '0 0 0 0' were required on systems
that dump core when NULL is dereferenced but this problem showed itself in
modern systems even with the 4 '0 0 0 0'. He also fixed the code so that the
generated fibonacci.c actually works; before it just printed 0 over and over
again (since it did not work anyway a segfault prevention was added here). He
also some array addressing (some of which might not be strictly necessary but as
he was testing the fibonacci.c bug he ended up changing it anyway). Finally he
changed this program to use fgets() not gets() to make it safer and to
prevent a warning about gets() at linking or runtime. Thank you Cody for your
assistance!
Yusuke Endoh pointed out that atof nowadays
needs #include <stdlib.h> which was used in order to get this to work
initially. Thank you Yusuke!
To run:
./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)
NOTE: this entry will segfault on no arg specified.
Try:
./theorem y 0 1 0.1 1
Judges' comments:
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, 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 comments:
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.
Copyright and CC BY-SA 4.0 License:
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/