A simple fsolve problem from a MATLAB beginner

Question

Peter J 2015-1-23

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/171254-a-simple-fsolve-problem-from-a-matlab-beginner

评论： Peter J 2015-1-23

Hi. I would like to solve a nonlinear equation using fsolve. The variable is denoted as phi. It should have three roots. Below is the mfile that I built.

function out = underwoodroot(phi)
alphaD = 1.00; alphaC = 2.5; alphaB = 6.25; alphaA = 15.625; xAfeed = 0.25; xBfeed = 0.25; xCfeed = 0.25; xDfeed = 0.25;
out = alphaA*xAfeed/(alphaA-phi)+alphaB*xBfeed/(alphaB-phi)+alphaC*xCfeed/(alphaC-phi)+alphaD*xDfeed/(alphaD-phi);
phi1 = fsolve(@underwoodroot,(alphaB+alphaA)/2)
phi2 = fsolve(@underwoodroot,(alphaC+alphaB)/2)
phi3 = fsolve(@underwoodroot,(alphaD+alphaC)/2)
end

However, when I tried to run it, MATLAB returned a "Not enough input arguments" comment. I wonder what happened to my code. As a MATLAB beginner, I would really appreciate any help you have. Thank you so much in advance!

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Answer 1

Shoaibur Rahman 2015-1-23

1
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https://ww2.mathworks.cn/matlabcentral/answers/171254-a-simple-fsolve-problem-from-a-matlab-beginner#answer_165675

在 MATLAB Online 中打开

Define underwoodroot function separately, and call them from another m-file.

In one m-file, write the following code, and save and run:

alphaD = 1.00; alphaC = 2.5; alphaB = 6.25; alphaA = 15.625;
phi1 = fsolve(@underwoodroot,(alphaB+alphaA)/2)
phi2 = fsolve(@underwoodroot,(alphaC+alphaB)/2)
phi3 = fsolve(@underwoodroot,(alphaD+alphaC)/2)

In another m-file, write the underwoodroot function, and save as underwoodroot.m

function out = underwoodroot(phi)
alphaD = 1.00; alphaC = 2.5; alphaB = 6.25; alphaA = 15.625; xAfeed = 0.25; xBfeed = 0.25; xCfeed = 0.25; xDfeed = 0.25;
out = alphaA*xAfeed/(alphaA-phi)+alphaB*xBfeed/(alphaB-phi)+alphaC*xCfeed/(alphaC-phi)+alphaD*xDfeed/(alphaD-phi);

However, if you want to keep them in a single m-file, then use two functions names, like below. Save the m-file as myFunction.m and run that.

function myFunction
alphaD = 1.00; alphaC = 2.5; alphaB = 6.25; alphaA = 15.625;
phi1 = fsolve(@underwoodroot,(alphaB+alphaA)/2)
phi2 = fsolve(@underwoodroot,(alphaC+alphaB)/2)
phi3 = fsolve(@underwoodroot,(alphaD+alphaC)/2)
function out = underwoodroot(phi)
alphaD = 1.00; alphaC = 2.5; alphaB = 6.25; alphaA = 15.625; xAfeed = 0.25; xBfeed = 0.25; xCfeed = 0.25; xDfeed = 0.25;
out = alphaA*xAfeed/(alphaA-phi)+alphaB*xBfeed/(alphaB-phi)+alphaC*xCfeed/(alphaC-phi)+alphaD*xDfeed/(alphaD-phi);