Finding multiple x values in plot for given y

I have to find the values for x when y=0 but i cant seem to make it work. I have tried with interp1 but it seems that it gives me an answer of x=2.3490 which is clearly wrong,since there are 2 points in the plot where y=0. Here's the code:

x = [0:0.001:pi]
f = exp(x/4).*sin(x)-1;
plot(x,f)
xlabel('Axis x');
ylabel('Axis y');
newLim = get(gca,'XLim'); 
newx = linspace(newLim(1), newLim(2), 30); 
set(gca,'XTick', newx);

% what I tried:
yi = 0 ;
xi = interp1(f,x,yi) ;
hold on
semilogy(xi,yi,'*r')

[Geroge Papas]

Here is the plot that the code gives:

Answer 1

[Geroge Papas]

Welp I solved it! I used zero-crossings estimation code and got the index vectors i needed to find the values of x when y aproximates 0. Here is the finished code and graph:

x = [0:0.001:pi]
f = exp(x/4).*sin(x)-1;

zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);
zx = zci(f);

figure(1)
plot(x, f, '-r')
hold on
plot(x(zx), f(zx), 'bp')
hold off
grid
legend('f(x)', 'Approximate Zero-Crossings')

%x1=0.9180
%x2=2.5900

Answer 2

[Daniel Pollard]

I think you want fsolve. Give it a function handle and an initial starting point, and it'll tell you (approximately) what x gives f(x)=0.