for i=1:length(y)
    if isreal(y(i)) && y(i)>400 %ÅжÏy(i)ÊÇ·ñÊÇʵÊý£¬²¢ÇÒÊÇ·ñ´óÓÚ400
        fprintf(1, '%.9f\n', y(i));
    end
end

syms x y; %×¢ÒâÓõ½µÄ·ûºÅ¶¼ÒªÉùÃ÷Ò»ÏÂ
a=y+1;
b=y-1;

f=a*b+a+b*x+y+6*x+2;

%½â·½³Ìf=0
equation = [char(f) ' = 0'];
A=solve(equation, 'y');

%ÉÏÃæ½âµÃµÄ½á¹ûÊÇ
%A =
%  - x/2 - (x^2 - 16*x - 4)^(1/2)/2 - 1
%   (x^2 - 16*x - 4)^(1/2)/2 - x/2 - 1

%¶ÔÓÚ·ûºÅʽ×Ó£¬Ê¹ÓÃsubsº¯Êý´úÈëÊýÖµ

%×¢ÒâÉÏÃæµÄ·½³ÌÒòΪÓпª·½£¬ËùÒÔ²»Ò»¶¨Äܽâ³öʵÊý½â£¬ÕâÀïÖ±½ÓÈ¡Ò»¶ÎÓÐʵÊý½âµÄ
x = 20:80;
y1 = zeros(1, length(x)); %Ï°¹ßÉÏÑ­»·Ç°Ïȸø¶¨´æ´¢¿Õ¼ä
y2 = zeros(1, length(x));
for i=1:length(x)
    y1(i) = subs(A(1), x(i));
    y2(i) = subs(A(2), x(i));
end

plot(x, y1, 'b', x, y2, 'r');

x = 20:80;
Y= subs(A, x);
plot(x, Y(1, :), 'b', x, Y(2, :), 'r');

2Â¥: Originally posted by sudo at 2011-10-12 10:12:19:
Äã²»ÓÃÿ´Î¶¼·ÅÄÇô¶à·ÖÉÏÀ´µÄ...

(1)ʹÓÃisrealº¯ÊýºÍÑ­»·
[code]
for i=1:length(y)
    if isreal(y(i)) && y(i)>400 %ÅжÏy(i)ÊÇ·ñÊÇʵÊý£¬²¢ÇÒÊÇ·ñ´óÓÚ400
        fprintf(1, '%.9f ...