# How can i solve for this issue with the logical flow

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Mark Loui on 6 May 2021
Commented: Mark Loui on 6 May 2021
n=length(q);
coef=k*dt/dr;
q_new=zeros(n,1);
q(0)=0;
% for i=1:n+1
% q_new(i)=q(i)+(coef*(q(i+1)-(2*q(i))+q(i-1)));
% end
for i=1:n+1
term1=(q(i+1)*((r(i+1)+dr)/r(i)*dr));
term2=2*q(i)*(1/dr);
term3=q(i-1)*((r(i)-dr)/r(i)*dr);
qnew(i)=q(i)+(coef*(term1-term2+term3));
q_new=qnew(i);
end
Can someone please help me with this i cant seem to make it work, what can i do to make the the error of logical go away?
Array indices must be positive integers or logical values: %This is the error show

Chad Greene on 6 May 2021
I think the error is here:
term3=q(i-1)*((r(i)-dr)/r(i)*dr);
The first time through the loop, i=1, meaning i-1=0. There is no zeroth element of q. Which element of q are you trying to access?
Mark Loui on 6 May 2021
Hmm sounds good, i try and see thanks

R2020b

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