# $Author: saulius $
# $Revision: 9756 $
# $Date: 2022-02-08 07:40:51 +0000 (Tue, 08 Feb 2022) $

Determinants of the 2x2, 3x3 and 4x4 matrices
=============================================

INTRO
=====

Words MUST, MAY, SHALL, SHOULD, written in all capitals, should be
interpreted as specified in the RFC 2119 [1].

PROGRAM
=======

Write a Perl program that computes determinants for 2x2, 3x3 and 4x4
square matrices.

Program name:
det2-4

Program invocation:
det2-4 matrices*.dat

Input files are optional; if they are not provided, the program MUST
read from STDIN (i.e. it's design must follow the Unix filter
pattern).

DATA FORMATS
============

Input data
==========

-- All lines that start with a has symbol ("#", ASCII HEX 23) MUST be
   treated as comments and ignored;

-- All empty lines MUST be ignored;

-- All data lines MUST contain 4, 9 or 16 white space separated
   floating-point numbers following the conventional programming
   language (Perl, Pascal, C) syntax (e.g. 6.02e+23);

-- All other lines SHOULD be treated as errors.

Output data
===========

All data output MUST proceed to STDOUT.

-- The first line of the output MUST contain the program Id, as
   generated by Subversion keywords (or equivalent subsystems
   generated by other version control systems); the line MUST start
   with the has character ("#") and MAY NOT contain the dollar
   characters ("$", ASCII HEX 24);

-- The remaining lines MUST contain a single real number on a line,
   the determinant value for the matrix that was given on the
   corresponding input line.

ERROR HANDLING
==============

All error messages MUST be output to STDERR. If an error is detected,
a suitable non-zero status (exit) code MUST be returned.

The program MUST detect abnormal situation and report them. An
informative user-friendly error reporting should be used. IN
particular, the error message MUST contain: the program name, the
input file name where the error was detected (use '-' without the
quotes as a file name if your input is STDIN), input line number where
the error was detected; quoted example of the erroneous input. The
program MAY output error position in the first character where the
error was detected. The error messages should be informative and
permit user to fix the error.

Perl functions 'die' and 'warn', invoked with and without the "\n"
character at the end of the message are examples of acceptable error
reporting. The native Perl diagnostics (switched on by "use warnings")
and file conditions detected by "while(<>) {...}" construct SHOULD be
used for error reporting.

The program SHOULD attempt to recover from errors and SHOULD continue
its operation as long as possible.

The following conditions MUST be detected and reported:

-- missing, unreadable, unreachable files;

-- system read errors;

-- wrong number of matrix components on the line;

-- wrong input number format.

If the program detects wrong format of at least one input number, the
output result MUST be the "NaN" string (IEEE 754 Not-a-Number) [2];

If the program encounters floating point overflow condition while
processing a matrix, its output on that line MUST be "Inf" (IEEE 754
Infinity) with a relevant sign on the corresponding output line.

REFERENCES
==========

1. S. Bradner "Key words for use in RFCs to Indicate Requirement
   Levels" (1997) URL: https://tools.ietf.org/html/rfc2119 .

2. Wikipedia. IEEE 754 (2022) URL: https://en.wikipedia.org/wiki/IEEE_754
   [accessed 2022-02-08T09:01:44 EET].