How to find the X-coordinate of the plot knowing the Y-value?

I am carrying out the Fast Fourier Transform for a time series of data. I have found out the maximum value of the voltage amplitude. However, I want to find out at what frequency value do we get the maximum voltage amplitude. How do I get that? In this case the maximum voltage amplitude turns out to be 474.0488.

clc;
clear all;
close all;
a=load('12.0.txt');
e=abs(a(:,2));
N=length(e);
e_m = sum(e)/N;
E=e-e_m;
dftE=fft(E,N);
dftE=dftE(1:N);
max0=abs(dftE);
f=0.1:0.1:5000;
plot(f,max0)
xlabel('Frequency');
ylabel('Voltage Amplitude');
legend('FFT of a Voltage Signal');
axis([0 100 0 500])
grid on
b = max(max0)

[Adam]

doc max

shows that max has a second output, which is the index at which the maximum value occurs. Use this as an index into your frequency vector and that will give you the answer.

Answer 1

[Torsten]

[~,index] = max(max0);
frequency_value = f(index)

[Aditya Ramnarayan]

Thank You!