function s=numberUnits(n)
% 
% NUMBERUNITS(N) Converts a number to a representation with named units
% Includes: Atto, Femto, Pico, Nano, Micro, Milli, Kilo, Mega, Giga, Tera,
% Peta, Exa. Numbers outside of this range are not converted.
% S: is a formatted string
%
% Note: This function is not efficiently implemented, and serves only as an
% exercise for conditionals.

error(nargchk(1,1,nargin));

% save original units, and use absolute value until later
isneg = 0;
if (n < 0)
    n = abs(n);
    isneg = 1;
end

nNew = 0;
unit = '';
unitAbbr = '';
% if unit is less than 1, use appropriate scale (milli, micro, ...)
if (n < 1)
    if (n >= 1e-3)
        nNew = n * 1e3;
        unit = 'Milli';
        unitAbbr = 'm';
    elseif (n >= 1e-6)
        nNew = n * 1e6;
        unit = 'Micro';
        unitAbbr = 'mu';
    elseif (n >= 1e-9)
        nNew = n * 1e9;
        unit = 'Nano';
        unitAbbr = 'n';
    elseif (n >= 1e-12)
        nNew = n * 1e12;
        unit = 'Pico';
        unitAbbr = 'p';
    elseif (n >= 1e-15)
        nNew = n * 1e15;
        unit = 'Femto';
        unitAbbr = 'f';
    else
        nNew = n * 1e18;
        unit = 'Atto';
        unitAbbr = 'a';
    end
% otherwise, if unit >= 1, use other scale (kilo, mega, ...)
else
    % numbers between 1 and 999.99.. are not converted, and have no units
    if (n < 1e3)
        nNew = n;
        unit = '';
        unitAbbr = '';
    elseif (n < 1e6)
        nNew = n / 1e3;
        unit = 'Kilo';
        unitAbbr = 'k';
    elseif (n < 1e9)
        nNew = n / 1e6;
        unit = 'Mega';
        unitAbbr = 'M';
    elseif (n < 1e12)
        nNew = n / 1e9;
        unit = 'Giga';
        unitAbbr = 'G';
    elseif (n < 1e15)
        nNew = n / 1e12;
        unit = 'Tera';
        unitAbbr = 'T';
    elseif (n < 1e18)
        nNew = n / 1e15;
        unit = 'Peta';
        unitAbbr = 'P';
    else
        nNew = n / 1e18;
        unit = 'Exa';
        unitAbbr = 'E';
    end
end

% return original units
if (isneg)
    nNew = -nNew;
end

% formatted string; note that number 32 is the space character, and is only
% placed in the string to produce a space
% s is the returned value for this function
s = strcat(num2str(nNew), 32, unitAbbr, ' (', unit, ')');