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Index exceeds matrix dimensions error

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JaffaCakes
JaffaCakes on 21 Apr 2021
Commented: JaffaCakes on 21 Apr 2021
Hi, I'm running a 105x100 matrix, and it's in line 74 (indicated+attached) that index exceeds matrix dimensions, how can I fix this please?
clear all
format short g
M=100
N=105
tend=5
%Paramters
K=6;
P=0.005
L=201
S=0.2
I=0.3
rw=1
h0=30
c0=3.5
Q=-30
dr=(L-rw)/N
dt=tend/M
D=K/(2*S);
a=D*dt/dr^2
B=D*dt/dr;
y=dt/I*dr;
if dr<2*rw
display('dr<=2*rw')
end
while dr>2*rw
N=input('enter new N')
dr=(L-rw)/N
end
if a<=0.5
display('a<=0.50')
end
while a>=0.5
M=input('enter new M')
dt=tend/M;100
a=D*dt/dr^2
if a>=0.5
display('a not satisfied')
end
end
A=setupmatrix(N,M);
%Boundary conditions for h
A(:,1)=h0; %when t=0
A(N,:)=h0; %when r=L
A
for j=1:M
A(1,j+1)=A(1,j)+2*a*A(2,j)^2-2*a*A(1,j)^2 + (a-(B/2*rw))*(2*dr*Q)/(pi*rw*K)+(P*dt)/S;
end
A
%index into Matrix h
for j=1:M
for i=2:N-1
r=rw+(i-1)*dr ;
A(i,j+1)=A(i,j)+(a+(B/2*r))*A(i+1,j)^2-2*a*A(i,j)^2+(a-(B/2*r))*A(i-1,j)^2+P*dt/S ;
end
end
A
C=setupmatrix(N,M)
d=P*dt+(I-S)*(A(i,j+1)-A(i,j))
for i=1:N
r=rw+(i-1)*dr ;
C(i,1)=c0/(1+exp(-((r-180)/4)));
end
C(N,:)=c0;
for j=1:M
for i=1:N
q=(-K/2)*(A(i+1,j)-A(i,j)/dr); %LINE 74 ERROR
C(i,j+1)=-y*(q/A(i,j))*C(i+1,j)+(1+y*(q/A(i,j)))-d/I*(A(i,j))*C(i,j)
end
end
FUNCTION setupmatrix :
function A = setupmatrix(N,M)
A=zeros(1,M)
i=2:N
A(i,:)=zeros
end
  4 Comments
JaffaCakes
JaffaCakes on 21 Apr 2021
I see I'll try this one out. Thanks a lot :)

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Accepted Answer

David Hill
David Hill on 21 Apr 2021
for j=1:M
for i=1:N%changing to N-1 allows script to run
q=(-K/2)*(A(i+1,j)-A(i,j)/dr);%A is 105x101 and N=105; therefore, you are indexing A(106,j) on last loop of i (you cannot do that)
C(i,j+1)=-y*(q/A(i,j))*C(i+1,j)+(1+y*(q/A(i,j)))-d/I*(A(i,j))*C(i,j)
end
end
  1 Comment
JaffaCakes
JaffaCakes on 21 Apr 2021
Amazing makes sense now, Thanks very much :)

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