finding x of y

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soloby
soloby 2015-6-25
评论： soloby 2015-6-25
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

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Azzi Abdelmalek
Azzi Abdelmalek 2015-6-25
编辑：Azzi Abdelmalek 2015-6-25
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
  1 个评论
soloby
soloby 2015-6-25
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

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