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I have an error I got from using fsolve but I do not understand why.

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Rachel Ong
Rachel Ong 2021-12-6
评论： Rik 2021-12-6
clear all;
clc;
W = 1248.5*9.81;
S = 17.1;
K = 0.05;
CDe = 0.03;
h = 0;
[T, p, rho, speedsound] = atmos(h);
V = 100 % random speed for test
Tava = (4 * ( (7 + V/speedsound )*200/3 + h*(2*V/speedsound) - 11) )
% x(1) = CL
func_1 = @(x) ((x(1))^2)/K + Tava/W*x(1) -3*CDe ; % Condition for max RC
FUNC = @(x) [func_1(x)];
CL = fsolve(@(x) FUNC(x), [0])
CD = 0.03 + 0.05*CL^2
% x(2) = alpha
% x(3) = eledefl
func_2 = @(x) 6.44*x(2) + 0.355*x(3) - CL ; % CL
func_3 = @(x) 0.03 + 0.05*(6.44*x(2) + 0.355*x(3))^2 - CD ; % CD
FUNC = @(x) [func_2(x); func_3(x)];
X = fsolve(@(x) FUNC(x), [0 0])
%
% aoa = X(1)
% eledefl = X(2)
I can solve for x(1) but not x(2) and x(3).
I got this error "Index exceeds the number of array elements (2).", however I dont understand what it means.
How can I solve this?

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Rik
Rik 2021-12-6
编辑：Rik 2021-12-6
You have this in func_2: x(3). That means the x you're passing should be at least 3 elements long.
X = fsolve(@(x) FUNC(x), [0 0 0])
You should also replace clear all by clear or by clearvars.
  2 个评论
Rachel Ong
Rachel Ong 2021-12-6
I see! Thank you so much! I am confused as I thought if I used x(2) and x(3) it will be 2 variables.
Rik
Rik 2021-12-6
You are indexing a vector. The fact that you only use 2 of them later on is not relevant, as fsolve is not aware of this.

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