How do I get the values of x at y=0.67 and y=0.87

x=linspace(0,4,100);
  y=zeros(size(x));
  p=0.275;
  figure
  k=2.031;
   for i=1:numel(x)

    y(i)=(exp(-(p*(x(i)))^k));

     end

     axis([0 4 0 1.8])
    plot(x,y,'--')
    xlabel('x')
    ylabel('y')

How do I calculate the corresponding x value for any given y value.

Answer 1

[Rik]

You can reverse the formula with pen and paper (and maybe some Wolfram-Aplha), interpolate with a function like interp1, or solve the equation with solve. The first method doesn't really involve Matlab, and for the latter two the documentation should be self-explanatory. Nonetheless, if you have questions, you should of course feel free to post a comment here.

Answer 2

[Torsten]

x = (log(1/y))^(1/k)/p

Best wishes

Torsten.

[Kalyan Dash]

Most of the time the expressions are much complex. So back calculation is not possible. So I want to get the answer from graph.

Have a look at the following code

https://in.mathworks.com/matlabcentral/answers/105189-how-do-i-find-x-for-a-given-value-of-y#answer_114425

Here it works fine. But in my code the variable y is an array and the plot is done Vs x and y arrays. So above code is not working.

[Rik]

x = (log(1./y)).^(1/k)/p

Don't forget element-wise operations if you want to use arrays. And if the expression is too complex to reverse, use either of the other solutions I mentioned in my answer.