MATLAB: I wanted to find a x value for a specific value of y from the graph this code doesn’t seem to work , how do i correct it

Question

clc
ntime = dt1.data(1:596,2);%time(x axis)
ndt40 = dt1.data(1:596,4);%displacement (y axis)
adi = min(ndt40);%minimum displacement
tymadi = interp1(ndt40,ntime,adi);%time at minimum displacement
plot(ntime,ndt40)
axis([0 3 -4 4]);
grid on

Answer 1

[~,index] = min(ndt40);%minimum displacement
ntime(index) % minimum time