How to mark a specific point in matlab plot?

Hello,

I'm trying to mark a specific point on the curves when y = 0. Because I want to know the value of x when y = 0.

but I didn't succeed....

x = 0:0.01:66.03;

y=(3.7*(10*(x/66.03).^3-15*(x/66.03).^4+6*(x/66.03).^5)-1.86);

plot(x,y,'c-','LineWidth',3);

y1=0;

x1=interp1(x,y,y);

hold on;

semilogy(x1,y1,'*r')

Any idea on how to fix the problem?

Thank you in advance for your help!

Answer 1

[Voss]

To interpolate to find a value of x for a given value of y, treat y as the independent variable and x as dependent on y.

x = 0:0.01:66.03;
y=(3.7*(10*(x/66.03).^3-15*(x/66.03).^4+6*(x/66.03).^5)-1.86);
plot(x,y,'c-','LineWidth',3);
y1=0;
% x1=interp1(x,y,y);
x1=interp1(y,x,y1); % given x(y), find x(y1)
hold on;
semilogy(x1,y1,'*r')

[LIM MING HUI]

Thank you! It is works!

[Voss]

You're welcome!