In the absence of the data, getting an independent variable valuex ‘x’ from an dependent variable value ‘y’ is relatively straightforward.
Try soemthing like this —
x = linspace(0, 20, 201);
y = besselj(0, x);
yval = linspace(-0.2, 0.2, 6);
for k1 = 1:numel(yval)
zxi = find(diff(sign(y-yval(k1))));
for k2 = 1:numel(zxi)
idxrng = max(1,zxi(k2)-1) : min(numel(x), zxi(k2)+1);
xv(k1,k2) = interp1(y(idxrng), x(idxrng), yval(k1));
end
end
for k1 = 1:size(xv,1)
xv(k1,xv(k1,:)==0) = NaN;
end
figure
plot(x, y)
hold on
for k1 = 1:size(xv,1)
plot(xv(k1,:), ones(size(xv(k1,:)))*yval(k1), 's')
end
yline(yval, ':')
hold off
grid
xlabel('X')
ylabel('Y')
.
