help in fzero function

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ana take
ana take on 13 Jan 2017
Commented: Walter Roberson on 13 Jan 2017
Here x, y,teta are vectors. When I call the function fzero it shows this message:
fzero(@(t)shkruajek(x,y,1,3,teta,0.1,4,t),0)
Exiting fzero: aborting search for an interval containing a sign change
because NaN or Inf function value encountered during search.
(Function value at -2.54232e+306 is NaN.)
Check function or try again with a different starting value.
NaN
can you help me to determine where is the problem here??
function [ek]=shkruajek(x,y,i,j,teta,speed,R,t)
ek=sqrt(((x(i)+ speed*cos(teta(i)*t)) - (x(j) + speed*sin(cos(teta(j)*t))))^ 2+ ((y(i) + speed*sin(teta(i)*t)) - (y(j) + speed*sin(teta(j)*t))).^ 2)-R;
end
a=fzero(@(t)shkruajek(x,y,i,j,teta,speed,R,t),0);
  4 Comments
ana take
ana take on 13 Jan 2017
the response I got: ai = fzero(@(t)prova(R,t),0) Exiting fzero: aborting search for an interval containing a sign change because NaN or Inf function value encountered during search. (Function value at -8.581e+153 is Inf.) Check function or try again with a different starting value.
ai =
NaN
Walter Roberson
Walter Roberson on 13 Jan 2017
Note that only the newer versions of MATLAB support fzero on complex-valued functions.

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Accepted Answer

Walter Roberson
Walter Roberson on 13 Jan 2017
You only provided a single bound, 0, to fzero. It makes guesses about where to look, and it happens to probe at -2.54232e+306 . Something in the calculation there is resulting in NaN being produced.
My guess is that at -2.54232e+306 you have multiple sub-expressions come out as infinite, and that you end up with infinity minus infinity (or negative infinity plus positive infinity). infinity minus infinity is NaN.
You should be considering giving two element bounding vector to fzero instead of just a single location.

More Answers (1)

John Chilleri
John Chilleri on 13 Jan 2017
Edited: John Chilleri on 13 Jan 2017
Hello,
In addition to what Walter Roberson said as good practice, it would appear that your function does not have a root.
I say this because your t is only found within sine and cosine functions, and after fzero has tested one period then no other value of t will make a difference, so the fact that it does not find a root within one period and rather continues to eventually error at -2.5 e306 suggests there is no root.
Hope this helps!

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