fzero help please I need value of y...the complete code is as follows

Question

Nic 2013-4-19

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/72665-fzero-help-please-i-need-value-of-y-the-complete-code-is-as-follows

I wrote following code in matlab.

% declare global variables
global bcr vc locr rc rb wb
% define given parameters
bcr = 0.713; 
vc = 0.18; 
locr=0.092; 
rc = 0.056; 
rb = 0.008; 
wb = 1.19;
% compute the root of wc f(wc)=0.0 using fzer0 function
[y,fval,exitflag,output] = fzero('myfun_y',[0.008,0.056])

function file is as follows:

% function file to calculate value of y at which f(y) = 0.0 using fzero
function f = myfun_y(y)
% declare global variables
global locr rb vc rc wb bcr 
% define function f(y)
f1 = ((y-rb)/(locr*(locr-y)*(locr-rb)))+((1/locr^2)*log((y*(locr-rb))/(rb*(locr-y))));
f2 = (y*(locr-y))*((1.+vc)+(1.-vc^2)*(rc^2-y^2)/(rc^2+y^2));
f3 = wb*bcr;
f = f1*f2-f3;
end

*When I run, this code I got following message.

Error using fzero (line 233)
FZERO cannot continue because user supplied function_handle ==> myfun_y
 failed with the error below.
   Not enough input arguments.
Error in compute_y (line 22)
[y,fval,exitflag,output] = fzero('myfun_y',[0.008,0.056]) *

ANy idea, what is going on...I need value of y between 0.008 and 0.56...

*I am hating fzero now...it is giving me hard time.

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Answer 1

Walter Roberson 2013-4-19

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/72665-fzero-help-please-i-need-value-of-y-the-complete-code-is-as-follows#answer_82764

在 MATLAB Online 中打开

Experiment with replacing

[y,fval,exitflag,output] = fzero('myfun_y',[0.008,0.056])

with

[y,fval,exitflag,output] = fzero(@myfun_y, [0.008,0.056])

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Walter Roberson 2013-4-19

It is the log* that is the problem. Not enough input arguments to log.

Nic 2013-4-19

编辑：Nic 2013-4-19

在 MATLAB Online 中打开

Hi, I change log* ... and run the program... it is giving right value of y which is 0.008 when wb =0.0.... But when I change the value of wb to 1.0..I got following error message.... I need to solve this problem please help. thank you so much.

(when wb =1.0)** Error using fzero (line 274) The function values at the interval endpoints must differ in sign. Error in compute_y (line 23) [y,fval,exitflag,output] = fzero(@myfun_y,[0.008, 0.056])

(when wb =0.0)** y =

0.0080

fval =

0

exitflag =

1

output =

    intervaliterations: 0
            iterations: 0
             funcCount: 2
             algorithm: 'bisection, interpolation'
               message: 'Zero find terminated.'

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