Find X value corresponding to Y value in a equation and find doesn't help as the y vector doesn't contain the exact value.

Hi everybody,

I am noob, so please help me out.

I am trying to find the beamwidth of a rectangular patch antenna. I have plotted the equations, but i have to find the value of x corresponding to the value at y=0.5. The function 'find' doesn't help as there is no exact value of y at 0.5. The result is a 1-by-0 empty matrix, which i guess is a null.

interp1 also doesn't help as I dont know the x-value.

So can you help me out?

Answer 1

[Matt J]

You should be interpolating with y as the domain and x as the range

 xi =interp1(y,x,0.5)

[Rachel Kufakunesu]

Thank you Matt J. After searching high and low, your answer solved my problem!

Answer 2

[Thorsten]

Sample function

x = 0:0.1:1;
y = x.^2;

Find approximative solution for y = 0.5

a = abs(y - 0.5);
ind = find(a == min(a));

Find exact solution with the approximative solution as starting value

fzero(@(x)(x^2 - 0.5), x(ind))