What wrong in line 12 ?? help me please (Index exceeds matrix dimensions.)

clear

close all;

N=10;

h = 0.5;

u1(1)= 2 ;

u2(1)= 3 ;

u3(1)=0 ;

t(1) = 0;

for n=1:N

u3(n+1)=u1(n)+h*u2(1);

u1(n+1)=u1(n)+1/2*(4*exp(0.8*t(n))-0.5*u1(n)+4*exp(0.8*t(n+1))-0.5*u3(n));

t(n+1)= t(n) + h ;

end

plot(t,u1);

Answer 1

[Alex Mcaulley]

In this line:

u1(n+1)=u1(n)+1/2*(4*exp(0.8*t(n))-0.5*u1(n)+4*exp(0.8*t(n+1))-0.5*u3(n));

the length of t is n, then t(n+1) gives an error

[Bui Thien Phuc]

Can you help t how t add when t = 1 so the t in the second equation exp(0.8*t(n+1))-0.5*u3(n)); double ??

[Alex Mcaulley]

I don't know what you are trying to solve. Without more information, probably you need to change the order:

clear
close all;
N=10;
h = 0.5;
u1(1)= 2 ;
u2(1)= 3 ;
u3(1)=0 ;
t(1) = 0;
for n=1:N
    u3(n+1)=u1(n)+h*u2(1);
    t(n+1)= t(n) + h ;
    u1(n+1)=u1(n)+1/2*(4*exp(0.8*t(n))-0.5*u1(n)+4*exp(0.8*t(n+1))-0.5*u3(n));
end
    plot(t,u1);

[Bui Thien Phuc]

Hey I want to use u2(1) only one time in first circle so I did right ?

[Alex Mcaulley]

Then, a better option is

clear
close all;
N=10;
h = 0.5;
u1 = zeros(1,N+1);
u2 = zeros(1,N+1);
u3 = zeros(1,N+1);
u1(1)= 2 ;
u2(1)= 3 ;
t = 0:h:h*N;
for n=1:N
    u3(n+1)=u1(n)+h*u2(n);
    u1(n+1)=u1(n)+1/2*(4*exp(0.8*t(n))-0.5*u1(n)+4*exp(0.8*t(n+1))-0.5*u3(n));
end
    plot(t,u1);

[Bui Thien Phuc]

just answer me I want to use u2(1) only one time in first circle so I did right ?

[Torsten]

If you use your code: no.

If you use Alex's second code: yes.

Answer 2

[Torsten]

clear
close all;
N = 10;
h = 0.5;
u1(1) = 2 ;
u2(1) = 3 ;
u3(1) = 0 ;
t = 0:h:N*h;
for n = 1:N
   u3(n+1) = u1(n)+h*u2(1);
   u1(n+1) = u1(n)+1/2*(4*exp(0.8*t(n))-0.5*u1(n)+4*exp(0.8*t(n+1))-0.5*u3(n));
end
plot(t,u1);