find zero of a custom function
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Hello, I would like to know if it is possible to use fzero for a custom function written using a script. For example: let us suppose I have defined a function f.m which takes 3 arguments f(x,y,z) I know the values of x and y and I want to find the value of z which returns the value of my function 0,
is it possible to use fzero ? if yes could you post a very simple example?
Thanks you Paolo
采纳的回答
John D'Errico
2013-12-7
First of all, do NOT use inline functions. They are slow, a hack given to us in the days before function handles were provided.
Pt1=0.999970474084335;
zcb=0.005646500819616;
rate=0.0056460;
tau2=0.99722222222222;
% a better fun. See that since all parameters but
% y are known, the function handle uses those values.
% I could also have written fun as a function of 5
% parameters, and then reduced it to a single variable
% function using a function handle in the call to zero.
fun = @(y) -Pt1+y+(zcb+(rate*tau2*y));
Next, plot the function!!!!!!!!!! Always do this.
ezplot(fun)
grid on
As you can see, there is clearly a root, just under 1.
ysol = fzero(fun,[0,2])
ysol =
0.988756958482095
fun(ysol)
ans =
-1.04083408558608e-17
Anyone who claims this was not a root should learn to read scientific notation. So I'm not at all sure what you did wrong, but it looks like you used some inaccurate value in the computation.
2 个评论
Paolo
2013-12-7
Brett Cooper
2017-11-16
Hello, would this method also work for a 2D custom function to find its zeros? In my case, I expect the function to be zero on a line...
更多回答（1 个）
Walter Roberson
2013-12-5
fzero( @(z) f(x, y, z), InitialGuessGoesHere )
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