How to use fzero and choose correctly initial guess?
21 views (last 30 days)
Show older comments
Hi,
May I know how to solve the following equation with fzero and get two numbers: -2 and +2.
When I used the following code, it returned x=-2
fzero(@(x) x^2-4,0)
And this returned x=+2
fzero(@(x) x^2-4,1)
And furthermore, how can I choose correctly the initial guess number? I found that the answer will depend on the initial guess.
0 Comments
Accepted Answer
Star Strider
on 26 Oct 2014
Whenever I have a function I want to use fzero with, I plot it to see how many zeros it has and about where they are. I then choose my initial estimates based on that.
A more mathematically correct approach involves taking the vector you want the zeros of, then multiplying it by a one-position circularly-shifted version of itself, using the circshift function. This produces negatives at the zero crossings that are easy to test for and determine the indices of using the find function. I then use the x-values at those indices as the initial estimates. The initial estimates don’t have to be perfect, just close enough. If there are several zero-crossings, you will get several answers from fzero. It is up to you to choose the ‘correct’ zeros.
4 Comments
More Answers (0)
See Also
Categories
Find more on Optimization in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!