在MATLAB上用fzero求解隐式方程 [英] solution of an implicit equation with fzero on MATLAB

问题描述

我一直在尝试通过在MATLAB中使用fzero来求解该隐式方程.保存代码的文件名为"colebrook"，到目前为止，我键入的内容如下.

I've been trying to solve this implicit equation by using fzero in MATLAB. File that holds the code is named as "colebrook" and I've typed so far is as below.

D = input('Please enter the pipe diameter in meters: ');
V = input('Please enter the fluid velocity in m/s: ');
rho = input('Please enter fluid density in kg/m^3: ');
mew = input('Please enter fluid viscosity in kg/m*s: ');
Re = D*V*rho/mew;

eps = input('Enter absolute roughness in milimeters: ');
eD = eps/(D*1000);

a = fzero(colebrookfunc,0.1);
fprintf(a);

我要求解的方程式保存在另一个名为"colebrookfunc"的m文件中，其包含的代码如下.

Equation that I want to solve is kept in another m-file called "colebrookfunc", and the code it contains is as below.

function F = colebrookfunc(x)
    F = x - 1./(-4 * log10(eD/3.7 + 1.256./(Re*x.^0.5))).^2;

我在跑步时遇到此错误:

When i run in i get this error(s):

??? Input argument "x" is undefined.

Error in ==> colebrookfunc at 2
F = x - 1./(-4 * log10(eD/3.7 + 1.256./(Re*x.^0.5))).^2;
Error in ==> colebrook at 28
a = fzero(colebrookfunc,0.1);

我怎么了?

谢谢.

推荐答案

您必须通过colebrookfunc作为

You have to pass colebrookfunc as a function handle. Also, unless you define colebrookfunc as a nested function (which you, apparently, don't), you need to somehow pass the parameters to the function.

因此，您对fzero的呼叫应如下所示:

Thus, your call to fzero should look like:

a = fzero(@(x)colebrookfunc(x,eD,Re),0.1)

coolebrookfunc的第一行必须是

function F = colebrookfunc(x,eD,Re)

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