MATlab code line doesnt run

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Oskar Kinat
Oskar Kinat 2021-3-31
回答： Neeraj Rajpurohit 2021-4-7
I am having the following MATlab code and keep running into the error of my xdot(i) line.
Error: Check for missing argument or incorrect argument data type in
call to function 'R'.
Error in 360Second (line 14)
xdot(i)=[x(3);x(4);-u*x/R(i)^3;-u*y/R(i)^3];
can you please check if you see anything else wrong with it after I fix that error.
a= 7000;
e= 0.1;
time= (60*60*24);
u= 3.986*10^5;
dt=0.1;
t=(0:.1:86400);
Rp= a*(1-e);
Vp=sqrt(u*(2/Rp-1/a));
x=zeros(4);
x=[Rp;0;0;Vp];
i=1;
while t(i)<=86400
xdot(i)=[x(3);x(4);-u*x/R(i)^3;-u*y/R(i)^3];
x=x+xdot*dt;
i=i+1
R(i)=sqrt(x(1)^2+x(2)^2);
V(i)=sqrt(x(3)^2+x(4)^2);
E(i)=V(i)^2/2-u/R(i);
end
plot(R,t);
plot(V,t);
plot(E,t);
title('random'), xlabel('random'), ylabel('random');
grid on
  7 个评论
显示 5更早的评论
the cyclist
the cyclist 2021-3-31
You don't define the variable y anywhere in this code, so it does not run for me.
Can you please upload the complete code, and first verify that it gives the error you are getting.
Oskar Kinat
Oskar Kinat 2021-3-31
I' am sorry I just added the y=0 I believe thats right.
a= 7000;
e= 0.1;
time= (60*60*24);
u= 3.986*10^5;
dt=0.1;
t=(0:.1:86400);
y=0;
R= [Rp,0];
Rp= a*(1-e);
Vp=sqrt(u*(2/Rp-1/a));
x=zeros(4);
x=[Rp;0;0;Vp];
i=1;
while t(i)<=86400
R(i)=sqrt(x(1)^2+x(2)^2);
xdot(i)=[x(3);x(4);-u*x/R(i)^3;-u*y/R(i)^3];
x=x+xdot*dt;
i=i+1
V(i)=sqrt(x(3)^2+x(4)^2);
E(i)=V(i)^2/2-u/R(i);
end
plot(R,t);
plot(V,t);
plot(E,t);
title('random'), xlabel('random'), ylabel('random');
grid on

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回答（1 个）

Neeraj Rajpurohit
DISCLAIMER: These are my own views and in no way depict those of MathWorks.
Greetings,
I see that you are accessing arrays R, V and E, without initialization in the line .To make the given script work, you will have to do the initialization of these variables. Also, to access the variables with indices, you will have to preallocate the arrays with appropriate sizes.

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