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

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?

Answer 1

[Rik]

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.

[Rachel Ong]

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]

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.