SIunits.m

function [factor,prefix] = SIunits(x)
% [factor,prefix] = SIunits(x)  
% The factors and suffixes supported are:
% 1e-3	m	milli		1e3	k	kilo
% 1e-6	u	micro		1e6	M	mega
% 1e-9	n	nano		1e9	G	giga
% 1e-12	p	pico		1e12	T	tera
% 1e-15	f	femto		1e15	P	peta
% 1e-18	a	atto		1e18	E	exa			
% 1e-21	z	zepto		1e21	Z	zeta
% 1e-24 y	yocto		1e24	Y	yotta
prefixes_n = {'m';'u';'n';'p';'f';'a';'z';'y'};
prefixes_p = {'k';'M';'G';'T';'P';'E';'Z';'Y'};
factor = ones(size(x));
prefix = cell(size(x));
for i = 1:length(x)
    if x(i)~=0
        p = floor( log10( abs(x(i)) ) / 3 + eps);
    else
        p = 0;
    end
    if p>0
        p = min(p,length(prefixes_p));
        prefix{i} = prefixes_p{p};
        factor(i) = 10^(3*p);
    elseif p<0
        p = min(-p,length(prefixes_n));
        prefix{i} = prefixes_n{p};
        factor(i) = 10^(-3*p);
    else
        prefix{i} = '';
        factor(i) = 1;
    end
end