From: Ruby Quiz <james@...>
Date: 2005-09-09T22:06:46+09:00
Subject: [QUIZ] NDiff (#46)

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by Bill Kleb

This week's quiz is to write a version of the diff command that compares files
numerically.  In Unix-speak, 

	$ ndiff --help
	Usage: ndiff [options] file1 file2

	Numerically compare files line by line, numerical field by numerical field.

	-d INT  --digits INT     Maximum number of significant digits that
	                         should match. (default: 0)
	-h      --help           Output this help.
	-q      --quiet          No output, just exit code.
	-s      --statistics     Provide comparison statistics only. (extra credit)
	-t DBL  --tolerance DBL  Tolerate <= DBL distance between numbers.
	                         (default: 0.0)

For example, given fileA,

	1.000001
	2.00
	-3
	Cy=0.11278889E-01  Cx=-1.343e+02

And fileB,

	1.000000
	1.99
	-3.4
	Cy=0.11278890E-01 Cx=-1.343e+02

the following scenarios could play out:

	$ ndiff fileA fileB
	1,4c1,4
	< 1.000001
	< 2.00
	< -3
	< Cy=0.11278889E-01  Cx=-1.343e+02
	---
	> 1.000000
	> 1.99
	> -3.4
	> Cy=0.11278890E-01 Cx=-1.343e+02
	
	$ ndiff -t 0.000001 fileA fileB
	2,3c2,3
	< 2.00
	< -3
	---
	> 1.99
	> -3.4
	
	$ ndiff --tolerance 0.01 fileA fileB
	3c3
	< -3
	---
	> -3.4
	
	$ ndiff --digits 1 fileA fileB  (zero exit code)
	
	$ ndiff -q fileA fileB  (non-zero exit code)

and, for extra credit,

	$ ndiff --statistics fileA fileB
	Numbers compared: 5
	Distance range: 0.0..0.4
	Average distance: 0.99987e-01 [guess]
	Mean distance: 1.0e-06 [guess]

FWIW, the results of this quiz will be used by NASA's FUN3D
team for regression testing aerothermodynamic simulation
software.