# Plotting ode 45 results

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imran shaikh 2021 年 10 月 9 日

Matlab 2020B was used to draft code:
Question
Drafted Code:
function [f] = twobody (t,X)
% Designed to call two body eqautions of motion
%x(1)= x position;
%x(2)= y position;
%x(3) = z position;
%x (4) = x velocity;
%x (5) = y velocity;
%x (6) = z velocity;
mu = 398600; % km^3/s^2
f = zeros (size(X));
Xdot(1:3) = X (4:6);
r=norm(X(1:3));
Xdot(4:6)= (-mu/r^3)*X(1:3);
end
Script file:
R0 = [6510.75956901532 2676.16546382759 333.33402937319]; %km. Transpose of column matrix
V0 = [-2.23202460862428 9.49860960555864 1.18311436869621]; % Km/s. Transpose of column matrix
X0= [R0,V0]; % Column vector input to ODE45
options=odeset; options = odeset('RelTol',1e-12,'AbsTol', 1e-12);
t = [0:10:86400]; % 24hrs converted to sec with 10 sec step size
[t,X]=ode45(@twobody,t,X0,options);
clear all
plot(t,R0);
xlabel('Time(seconds)');
Error message:
Unrecognized function or variable 't'.
Error in twobodyscript (line 9)
plot(t,R0);
Can someone help resolve the error message and help plot the three plots? and i am not sure how to approach below question yet, some help would be greatly appreciated.
##### 1 件のコメント表示非表示 なし
Stephen 2021 年 10 月 9 日
Note that inside your function the output f is always just an array of zeros, while the variable Xdot is totally unused.

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### 回答 (1 件)

Stephen 2021 年 10 月 9 日

clear all % <- get rid of this.
It seems that the main purpose of CLEAR ALL is to introduce bugs into beginners' code when they use it totally inappropriately, e.g. at the start of every script or in the middle of their code:
##### 3 件のコメント表示非表示 2 件の古いコメント
Stephen 2021 年 10 月 9 日
Making a few guesses about the meaning of your variables, perhaps something like this:
R0 = [6510.75956901532,2676.16546382759,333.33402937319]; % km
V0 = [-2.23202460862428,9.49860960555864,1.18311436869621]; % Km/s
Op = odeset('RelTol',1e-12,'AbsTol', 1e-12);
ts = 0:10:86400; % 24hrs converted to sec with 10 sec step size
[t,Y] = ode45(@twobody,ts,[R0,V0],Op);
plot(t,Y(:,1:3));
xlabel('Time (seconds)'); function Xdot = twobody (t,X)
mu = 398600; % km^3/s^2
Xdot = zeros(size(X));
Xdot(1:3) = X(4:6);
r = norm(X(1:3));
Xdot(4:6)= (-mu/r^3)*X(1:3);
end

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