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invalid index in program

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shiv gaur
shiv gaur 2022-2-24
关闭： Rik 2022-2-24
Ran in:
p=8/3;
r=25;
sigma=10;
npoints =5000;
dt = 0.1;
a = zeros(npoints,1);
b = zeros(npoints,1);
c= zeros(npoints,1);
t = zeros(npoints,1);
//t=1:dt:100;
Invalid use of operator.
a(1)=1;
b(1)=1;
c(1)=1;
suma=0;
sumb=0;
sumc=0;
sumS=0;
sumZ=0;
for i = 1:npoints-1
sumS=sumS+a(i)*c(i-npoints);
sumZ=sumZ+a(i)*b(i-npoints);
a(i+1)=((sigma)/(i+1))*(b(i)-a(i));
b(i+1)=(1/(i+1))*(r*a(i)-b(i)-sumS);
c(i+1)=(1/(i+1))*(sumZ-p*c(i));
suma=suma+a(i).*(t^i);
sumb=sumb+b(i).*(t^i);
sumc=sumc+c(i).*(t^i);
t(i+1) = t(i) + dt;
end;
plot(t,suma)
pl revise the program
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shiv gaur
shiv gaur 2022-2-24
sorry jan this is edit program that is running program this is the program of lorenz using time step
we have to plan match with below program using power series now program is right
p=8/3;
r=25;
sigma=10;
npoints =500000;
dt = 0.0001;
a = zeros(npoints,1);
b = zeros(npoints,1);
c = zeros(npoints,1);
time = zeros(npoints,1);
a(1)=1;
b(1)=1;
c(1)=1;
for step = 1:npoints-1
a(step+1)=a(step)+sigma*(b(step)-a(step))*dt;
b(step+1)=b(step)+(-a(step)*c(step)+r*a(step)-b(step))*dt;
c(step+1)=c(step)+(a(step)*b(step)-p*c(step))*dt;
time(step+1) = time(step) + dt;
end;
subplot (2,1,1);
plot(time,z,'b' );
xlabel('time');
ylabel('z');
subplot (2,1,2);
plot (x,z,'g' );
xlabel('x');
ylabel('z')
2.power series
p=8/3;
r=25;
sigma=10;
npoints =5000;
dt = 0.1;
a = zeros(npoints,1);
b = zeros(npoints,1);
c= zeros(npoints,1);
t = zeros(npoints,1);
a(1)=1;
b(1)=1;
c(1)=1;
suma=0;
sumb=0;
sumc=0;
sumS=0;
sumZ=0;
for i = 1:npoints-1
sumS=sumS+a(i)*c(i-npoints);
sumZ=sumZ+a(i)*b(i-npoints);
a(i+1)=((sigma)/(i+1))*(b(i)-a(i));
b(i+1)=(1/(i+1))*(r*a(i)-b(i)-sumS);
c(i+1)=(1/(i+1))*(sumZ-p*c(i));
suma=suma+a(i).*(t^i);
sumb=sumb+b(i).*(t^i);
sumc=sumc+c(i).*(t^i);
t(i+1) = t(i) + dt;
end;
plot(t,sumb)
why not giving match plot
Rik
Rik 2022-2-24
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Click the link Jan gave you. Also click this.
Feel free to reopen the question and edit your last comment.

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回答（2 个）

Walter Roberson
Walter Roberson 2022-2-24
npoints =5000;
for i = 1:npoints-1
sumS=sumS+a(i)*c(i-npoints);
First iteration: i is 1, and a(1) is being indexed; as you initialized a(1) that is valid so far.
Then c(i-npoints) is being indexed. That is c(1-5000) which is c(-4999) which is not a valid index.
Jan
Jan 2022-2-24
Use the debugger to examine the cause of problems. Type this in the command window:
dbstop if error
Run the code again until it stops at the error.
A guess: c(i-npoints) cannot work, because the index is negative.

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