help with fzero function

Question

Ziqiang Gao 2016-4-5

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/277168-help-with-fzero-function

评论： John D'Errico 2016-4-5

Hi,I don't know why this is not correct. Could you please help me to modify it.

phi=3+t1;
beta=2*t1;
fun=@(t1) phi-beta;
x0=[1 9];
z=fzero(fun,x0);
disp(z)
----------------
and the command window  shows
Error using fzero (line 242)
Function values at interval endpoints must be finite and real.
Error in Untitled (line 5)
z=fzero(fun,x0);

Please help. Thank you very much. If you can make it correct, I will really appreciate this.

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Answer 1

Star Strider 2016-4-5

1
链接

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https://ww2.mathworks.cn/matlabcentral/answers/277168-help-with-fzero-function#answer_216442

在 MATLAB Online 中打开

You have to make anonymous functions out of ‘phi’ and ‘beta’, and then refer to them as functions in the fzero call:

phi = @(t1) 3+t1;
beta = @(t1) 2*t1;
fun=@(t1) phi(t1)-beta(t1);
x0=[1 9];
z=fzero(fun,x0);
disp(z)

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John D'Errico 2016-4-5

在 MATLAB Online 中打开

Think of it like this. As you wrote it, phi is NOT a function. It is a simple variable that takes on some known value, as long as t1 is already defined.

phi=3+t1;
beta=2*t1;

So, whatever t1 was at that point, phi is just a number, NOT a function. Had t1 not been defined before that point, MATLAB would have generated an error, telling you that t1 was undefined.

As Star points out, you can explicitly define phi and beta as functions of some parameter (call it t1), and then use them in the function fun.

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