How do I get my code to display the associated x values for maximum and minimum

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cakey 2014-9-21

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/155682-how-do-i-get-my-code-to-display-the-associated-x-values-for-maximum-and-minimum

评论： Matt J 2014-9-22

In addition, How do I get it to label the coordinates in the graph it makes? I tried getting it to display Xmax or Xmin, but it says not defined.

a = -7.0;
b = 1.0;
c = 2.0;
d = 20.0;
e = 2.0;
f = 5.0;
p = @(x) c * x.^3 + d * x.^2 + e * x + f;
CP = quadratic(3 * c, 2 * d, e);
 crit_pt1 = CP(1);
 crit_pt2 = CP(2);
if isreal(crit_pt1)
  disp('Crit Point 1:');
  disp(crit_pt1);
  disp('p(Crit Point 1):');
  disp(p(crit_pt1));
    disp('Crit Point 2:');
    disp(crit_pt2);
    disp('p(Crit Point 2):');
    disp(p(crit_pt2));
  else
    disp('The critical points are complex.');
  end
disp('Left Endpoint:');
disp(a);
disp('p(Left Endpoint):');
disp(p(a));
disp('Right Endpoint:');
disp(b);
disp('p(Right Endpoint):');
disp(p(b));
Q=[p(a),p(b),p(crit_pt1),p(crit_pt2)];
disp('p(Xmax):');
disp(max(Q));
disp('p(Xmin):');
disp(min(Q));
delta = (b - a) / 100;
x = a:delta:b;
y = p(x);
plot(x, y)