finding x of y

x = -10:0.1:10;
f1 = trapmf(x,[-2 0 0 2]);
index = find(f1 ==.05);
Xidx = x(index)

Why would Xidx give me an empty matrix 1-by-0?

I know for a fact that f1 has 0.05 at the 82nd iteration

Answer 1

[Azzi Abdelmalek]

Try this

x = -10:0.1:10;
f1 = trapmf(x,[-2 0 0 2])
index=find(abs(f1-0.5)<10^(-10))
Xidx=x(index)

And read this

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

[soloby]

this works perfectly, thanks.

One more question, if i wanted to do this for all values of f1, would a for loop be sufficient?

something like

 x = -10:0.1:10;
f1 = trapmf(x,[-2 0 0 2]);
for x = -10:0.1:10;
    f1 = trapmf(x,[-2 0 0 2])
    index=find(abs(f1-0.5)<10^(-10))
    Xidx=x(index)
end

I'm curious how you got the f1-0.5 < 10^-10 part.,

thanks