# Trying to code a state space modelling for thrust vector control of a rocket. I keep getting Error using plot, Invalid Data Argument, please help

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Chinmay Kundapur on 25 Jul 2022
Answered: Sam Chak on 26 Jul 2022
%% STATE SPACE MODELLING %%1%
clc;
close all;
clear all;
%-cosntant values
Iyy=2.186e8;
m=38901;
Tc=2.361e6;
v= 1347;
Cn_alpha=0.1465;
g= 26.10;
N_alpha=686819;
M_alpha=0.3807;
M_delta=0.5726;
x_cg=53.19;
x_cp=121.2;
F=Tc;
%Othr important constants
Mach=1.4 %mach
h=34000; %height of the launch
S=116.2,7 %Area of the platform
Fbase=1000; %base drag
Ca=2.4; %coefficients
D=Ca*680*3-Fbase; %-drag
Drag=7.15*D %total drag
%state space matrix
A_m=[0 1 0;M_alpha 0 M_alpha/v;-(F-Drag+N_alpha)/m 0 -N_alpha/(m*v)];
B_m=[0;M_delta;Tc/m];
C_m=diag([1 1 1])
D_m=[0; 0; 0]
pitch_ss= ss(A_m, B_m,C_m, D_m);
%%% COST FUNCTION %%%
%cost function
cvector={'bo' 'ro' 'go'};
R_vector=[ 0.1 5 10]
%lowest weight to TVC angle, max to drift
figure;hold on;
for k=1:1
R_matrix_drift=R_vector(k);
Q_matrix_drift=[1 0 1/v; 0 0 0;1/v 0 1/v^2];
[K S e] = lqr(pitch_ss,Q_matrix_drift,R_matrix_drift);
for i=1:10000
e_val( :,i ) =eig (A_m-B_m*K*i/10000);
end
plot(real(e_val(1,:)),imag(e_val(1,:)),cvector(k));
plot(real(e_val(2,:)),imag(e_val(2,:)),cvector(k));
plot(real(eval(3,:)),imag(e_val(3,:)),cvector(k));
grid;
end
xlim([-2 1]);
legend ('R=0.1') ;
%LQR Gains are obtained
K_1=K(1);
K_2=K(2);
K_3=K(3);

Walter Roberson on 25 Jul 2022
cvector{k} not (k). You cannot pass a cell array into plot, you have to dereference it
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P.V. PRANAV on 26 Jul 2022
Yet no result, the code is running but I do not see a plot?

Sam Chak on 26 Jul 2022
@Chinmay Kundapur, alternatively, you can directly write the color code straightaway.
Iyy = 2.186e8;
m = 38901;
Tc = 2.361e6;
v = 1347;
Cn_alpha = 0.1465;
g = 26.10;
N_alpha = 686819;
M_alpha = 0.3807;
M_delta = 0.5726;
x_cg = 53.19;
x_cp = 121.2;
F = Tc;
% Oth(e)r important constants
Mach = 1.4; %mach
h = 34000; %height of the launch
S = 116.27; %Area of the platform
Fbase = 1000; %base drag
Ca = 2.4; %coefficients
D = Ca*680*3-Fbase; %-drag
Drag = 7.15*D; %total drag
% state space matrix
A_m = [0 1 0; M_alpha 0 M_alpha/v; -(F-Drag+N_alpha)/m 0 -N_alpha/(m*v)];
B_m = [0; M_delta; Tc/m];
C_m = diag([1 1 1]);
D_m = [0; 0; 0];
pitch_ss = ss(A_m, B_m, C_m, D_m)
pitch_ss = A = x1 x2 x3 x1 0 1 0 x2 0.3807 0 0.0002826 x3 -77.63 0 -0.01311 B = u1 x1 0 x2 0.5726 x3 60.69 C = x1 x2 x3 y1 1 0 0 y2 0 1 0 y3 0 0 1 D = u1 y1 0 y2 0 y3 0 Continuous-time state-space model.
R_vector = [0.1 5 10];
% lowest weight to TVC angle, max to drift
figure; hold on;
for k = 1:1
R_matrix_drift = R_vector(k);
Q_matrix_drift = [1 0 1/v; 0 0 0; 1/v 0 1/v^2];
[K S e] = lqr(pitch_ss, Q_matrix_drift, R_matrix_drift);
for i = 1:10000
e_val( :,i ) = eig (A_m-B_m*K*i/10000);
end
plot(real(e_val(1,:)),imag(e_val(1,:)), 'bo');
plot(real(e_val(2,:)),imag(e_val(2,:)), 'ro');
plot(real(e_val(3,:)),imag(e_val(3,:)), 'go');
grid;
end
xlim([-2 1]);
legend ('R=0.1'); %LQR Gains are obtained
K_1 = K(1)
K_1 = 3.9108
K_2 = K(2)
K_2 = 3.7074
K_3 = K(3)
K_3 = 4.5886e-04