function p = polynom(a)
%POLYNOM多項(xiàng)式類構(gòu)造函數(shù)
%   p = POLYNOM(v) 從向量v創(chuàng)建一個多項(xiàng)式對象，包含按x降冪排列的系數(shù)。
if nargin == 0
   p.c = [];
   p = class(p,'polynom');
elseif isa(a,'polynom')
   p = a;
else
   p.c = a(:).';
   p = class(p,'polynom');
end