# How to solve the error "[t, z]= ode45(@observer, t_temp,z0)" in line 23.

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Meenakshi Tripathi on 19 Jan 2021
function will
clc
global E A B C N P L M x0 tspan u
E=[0.5 -2.5 0;3 -3 4;2 -1 3];
A=[-1 4.5 -0.5;-7 7 -8;-5 3 -6];
B=[1 0 1;0 1 1;1 0 -1];
C=[1 0 1];
N=[-0.75 -1 0.25;0 -2 0;0.25 1 -0.75];
L = [51.3257 11.2723;41.5581 7.8378;-24.3673 -6.2663];
M = [-0.4488 2.4167;-0.0898 0.4833;0.2693 -1.4500];
R = [0.3565 0.6582;0.1578 -0.2295;-0.3565 -0.6582]
B1= [-0.7306 -0.8299 -0.5319;0.4742 0.0304 1.3620]
P = R*B1
x0 = [1 0 -1];
tspan = 0:.1:20;
[x,y]=solbasic;
function dzdt = observer(t,z)
dzdt=N*z+L*[(y(i,:)+y(i+1,:))/2]'+P*u;
end
z0=[10 11 6];
for i = 1:length(y)-1;
t_temp =((i-1)/10):.05:(i/10);
[t,z]=ode45(@observer,t_temp,z0);
end
z1;
x;
x_cap=z+y*M';
e=x-x_cap;
end
function [x,y] = solbasic()
%y is the output which we will get after finding value of x
global E tspan x0 C
opt = odeset('RelTol',1e-6,'Mass',E);
[~, x] = ode15s(@basic, tspan, x0, opt)
y = x*C';
end
function dxdt = basic(t,x)
global A B u
u=[exp(-t)*sin(t);0.2*sin(2*t);0.2*sin(3*t)];
dxdt=A*x+B*u;
end
My errors are-
Error using odearguments (line 93)
WILL/OBSERVER must return a column vector.
Error in ode45 (line 115)
odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);
Error in will (line 23)
[t,z]=ode45(@observer,t_temp,z0);

Mischa Kim on 19 Jan 2021
dzdt seems to be a (3x2 ?) matrix. It needs to be a 3x1 vector to be consistent with the initial conditions, z0, which is also a 3-component vector.
function dzdt = observer(t,z)
dzdt = N*z + L*[(y(i,:)+y(i+1,:))/2]' + P*u;
end
Meenakshi Tripathi on 20 Jan 2021
it worked.

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