function Y=str2poly(X)
%X是字符串形式的多項式
%Y是行向量形式的多項式
%輸入格式檢查
if(ischar(X)==0) 
    disp('輸入錯誤：輸入X必須是一個字符串！');
end;
%用正則表達式尋找'+'或者'-'的下標(biāo)位置
index=regexp(X,'\+|\-');
%多項式的項數(shù)
L=length(index);
%用于存儲多項式每一項信息的單元字符串矩陣
term=cell(1,L+1);
term(1)=cellstr(X(1:(index(1)-1)));    
for i=1:L-1,
    term(i+1)=cellstr(X(index(i):(index(i+1)-1)));
end;
term(L+1)=cellstr(X(index(L):end));
%如果第一項為空，則刪除該項
if(isempty(char(term(1))))
    term(1)=[];
%多項式的項數(shù)減一   
    L=L-1;
end;  
%多項式系數(shù)矩陣
coefficient=[];
%多項式冪次矩陣，它與多項式系數(shù)矩陣一一對應(yīng)
power=[];
for i=1:L+1,
%單項多項式字符串表達式    
    substring=char(term(i));
%用正則表達式，尋找字符串'x^'，由于'^'是正則表達式中的特殊字符，多以用'\^'來表示    
    index2=regexp(substring,'x\^');
    if(isempty(index2)==0),
%如果匹配上后        
        if(index2(1)==1),
%單項多項式字符串為'x^*'形式            
            coefficient=[coefficient 1];
            power=[power str2num(substring((index2(1)+2):end))];
        elseif(index2(1)==2),   
%單項多項式字符串為'+x^*'或者'-x^*'，'3x^*'形式            
           if(substring(1)=='+'),
               coefficient=[coefficient 1];
               power=[power str2num(substring((index2(1)+2):end))];
           elseif(substring(1)=='-'),
               coefficient=[coefficient -1];
               power=[power str2num(substring((index2(1)+2):end))];
           else
               coefficient=[coefficient str2num(substring(1:(index2(1)-1)))];
                power=[power str2num(substring((index2+2):end))];
           end;          
        else
%單項多項式字符串為'2.2x^*'            
            coefficient=[coefficient str2num(substring(1:(index2(1)-1)))];
            power=[power str2num(substring((index2+2):end))]; 
        end;
    else
%單項多項式字符串不含'x^'        
%用正則表達式，尋找字符串'x'
        index2=regexp(substring,'x');
        if(isempty(index2)==0),
%如果匹配上'x'            
            if(index2(1)==1),
%單項多項式字符串為'x*'形式                
                coefficient=[coefficient 1];
                power=[power 1];               
            elseif(index2(1)==2), 
%單項多項式字符串為'+x*'或者'-x*'，'3x*'形式                 
               if((substring(1)=='+')==1),
                   coefficient=[coefficient 1];
                   power=[power 1];
               elseif(substring(1)=='-'),
                   coefficient=[coefficient -1];
                   power=[power 1];
               else
%單項多項式字符串為'2.2x*'                    
                   coefficient=[coefficient str2num(substring(1:(index2-1)))];
                    power=[power 1];
               end;              
            else
                
                coefficient=[coefficient str2num(substring(1:(index2-1)))];
                power=[power 1]; 
            end;
        else
%單項多項式字符串不含'x^','x',則斷定它是常數(shù)項
           coefficient=[coefficient str2num(substring)];
           power=[power 0]; 
        end;   
    end;
end;

N=max(power)+1;
Y=zeros(1,N);
for i=1:N,
    index3=find(power==(N-i));
    Y(i)=sum(coefficient(index3));
end;