How do I find and display the intersection of my functions?

Question

Mo_B 2017-1-10

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/319869-how-do-i-find-and-display-the-intersection-of-my-functions

回答： Star Strider 2017-1-10

采纳的回答： Star Strider

Bildschirmfoto 2017-01-10 um 20.22.14.png

在 MATLAB Online 中打开

Hi guys,

I want to find the intersection of y3 and y4,

   x=(0:0.5:80).';
y1=(0.02049/0.4)*x;
y2=(0.53*60./(1+(1.331./(sqrt(0.0631*x./(83.18-x))).^3)));
y3=(0.53*60./(1+(1.331./(sqrt(0.0631*x./(83.18-x))).^3)))-(0.02049/0.4)*x;
y4=(0.02049/0.4)*x-(0.53*60./(1+(1.331./(sqrt(0.0631*x./(83.18-x))).^3)));
figure
plot(x,y1,'r')
hold on 
plot(x,y2,'c')
plot(x,y3,'g')
plot(x,y4,'b')
legend('Line1','Line2','Line3','Line4')
axis([0 80 -1 3.5])

i tried to use

C = intersect(y3,y4)

I get C = 0, but I want the intersection near x = 70;

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Answer 1

Star Strider 2017-1-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/319869-how-do-i-find-and-display-the-intersection-of-my-functions#answer_250123

在 MATLAB Online 中打开

Try this:

x = linspace(0, 80, 200);
y3 = @(x) (0.53*60./(1+(1.331./(sqrt(0.0631*x./(83.18-x))).^3)))-(0.02049/0.4)*x;
y4 = @(x) (0.02049/0.4)*x-(0.53*60./(1+(1.331./(sqrt(0.0631*x./(83.18-x))).^3)));
y34 = @(x) y3(x) - y4(x);                           % Subtract Functions
x0 = 40;
xi = fzero(y34, x0);
figure(1)
plot(x, y3(x),  x, y4(x))
hold on
plot(xi, y3(xi), 'pr')
hold off
grid
xi =
    68.8010