function Metric = num2metric (number, arg2, arg3)

% Convert a numeric argument to a string rounded to a specified number of
% decimal digits with a metric prefix.

% Arguments:
%   number     required     quantity to be converted to a metric string
%   digits     optional     number of digits to the right of the decimal point
%   blank      optional     flag to include/suppress blank for no prefix
%
% If digits and blank are both specified then digits must precede blank



% Check and assign arguments
if (nargin == 1)
  digits = 3;
  blank = true;
  
elseif (nargin == 2)
  if (isnumeric (arg2))
    digits = arg2;
	blank = true;
  elseif (ischar (arg2))
    if (strcmp (arg2, 'blank'))
	  digits = 3;
	  blank = true;
	elseif (strcmp (arg2, 'noblank'))
	  digits = 3;
	  blank = false;
    else
      fprintf ('\nnum2metric: unexpected argument\n\n')
	end
  else
    fprintf ('\nnum2metric: unexpected argument\n\n')
  end
  
elseif (nargin == 3)
  if (isnumeric (arg2) && ischar (arg3))
    digits = arg2;
    if (strcmp (arg3, 'blank'))
	  blank = true;
	elseif (strcmp (arg3, 'noblank'))
	  blank = false;
    else
      fprintf ('\nnum2metric: unexpected argument\n\n')
	end
  else
    fprintf ('\nnum2metric: unexpected argument\n\n')
  end
  
else
  fprintf ('\nnum2metric: unexpected argument\n\n')

end



% Determine metric exponent
if (number == 0)
  exponent = 0;
else
  exponent = 3 * floor (log10 (abs (number)) / 3);
end
exponent = max (min (exponent, 24), -24);



% Determine mantissa
mantissa = round (number * 10^(digits-exponent)) / 10^digits;
if (abs (mantissa) == 1000 && exponent ~= 24)
  mantissa = sign (mantissa);
  exponent = exponent + 3;
end
Metric = num2str (mantissa);



% Zero padding
if (digits > 0)
  index = strfind (Metric, '.');
  if (isempty (index))
    Metric = [Metric '.'];
    index = length (Metric);
  end

  k = digits - length (Metric) + index;
  while (k > 0)
    Metric = [Metric '0'];
    k = k-1;
  end
end



% Append metric prefix
Prefixes = ['yzafpn' char(181) 'm kMGTPEZY'];
if (blank || exponent ~= 0)
  Metric = [Metric ' ' Prefixes(9+exponent/3)];
else
  Metric = [Metric ' '];
end

end