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Trying to find root of equation with fzero command in Matlab.

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Yianni
Yianni 2014-11-7
回答： Orion 2014-11-7
I want to solve a problem in which I am given a function (seen below) where W is 4.9 and I must find v. I have to use the fzero method but I am having trouble with this as I only know how to find the roots. How can I do this? (Function file and script file ARE separate and below)
function W = dforce(v)
R = 287;
P = 101300;
d = 15;
A = (pi*d^2)/4;
T = linspace(-60,60,121);
b1 = 2.156954157e-14;
b2 = -5.332634033e-11;
b3 = 7.477905983e-8;
b4 = 2.527878788e-7;
mu = b1*T.^3+b2*T.^2+b3*T+b4;
ro = P./(R*T);
Re = (ro*v*d)/mu;
Cd = (24/Re)+(6/(1+sqrt(Re)))+0.4;
W = Cd*0.5*ro*v^2*A;
end
___________________________________________________________________________________ clear all, close all
m = 0.5;
g = 9.8;
N = m*g;
dF = @(v) dforce(v)- N;
V = fzero(dF,0);

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回答（2 个）

Orion
Orion 2014-11-7
Why is T a vector ?
usually, fzero is used to solve an equation to find one scalar solution.
Orion
Orion 2014-11-7
that seems more logic for me.
use the syntax for using an extraparameter to your function.
% here's an example from the matlab documentation.
myfun = @(x,c) cos(c*x); % parameterized function
c = 2; % parameter
fun = @(x) myfun(x,c); % function of x alone
x = fzero(fun,0.1)
in your case, you should do something like
for T = linspace(-60,60,121);
dF = @(v) dforce(v,T)- N;
V = fzero(dF,0);
end

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