Index exceeds matrix dimensions

Hey guys I'm facing a problem with my codes. I keep getting the message 'index exceeds matrix dimensions' and I can't seem to find where the problem is. I'm very new to Matlab. These are the codes I used:

Tinf = 5;
dx = 0.25;
dy = 0.25;
h = input('input a value for h: ');
k = input('input a value for k: ');
iter = input('specify the number of iterations, n: ');
C1 = 2/k;
C2 = 2/(h*dx);
C3 = 1/k;
C4 = 1/(h*dx);
T1 = 20;
T2 = 22;
T3 = 26;
T4 = 32;
T5 = 36;
T6 = 40;
T7 = 42;
T8 = 45;
T9 = 48;
T10 = 50;
T11 = 20;
T12 = 30;
T13 = 35;
T14 = 40;
T15 = 45;
T16 = 50;
T17 = 55;
T18 = 60;
T19 = 70;
T20 = 80;
T21 = 20;
T22 = 56;
T23 = 60;
T24 = 65;
T25 = 72;
T26 = 76;
T27 = 80;
T28 = 84;
T29 = 88;
T30 = 92;

for n=1:iter

T1(n+1) = (((T2(n)/C1) + (5/C2)) / ((1/C1) + (1/C2)));
T2(n+1) = (((T1(n+1)/C1) + (T3(n)/C1) + (T12(n)/C3) + (5/C4)) / ((1/C1) + (1/C1) + (1/C3) + (1/C4)));
T3(n+1) = (((T2(n+1)/C1) + (T4(n)/C1) + (T13(n)/C3) + (5/C4)) / ((1/C1) + (1/C1) + (1/C3) + (1/C4)));
T4(n+1) = (((T3(n+1)/C1) + (T5(n)/C1) + (T14(n)/C3) + (5/C4)) / ((1/C1) + (1/C1) + (1/C3) + (1/C4)));
T5(n+1) = (((T4(n+1)/C1) + (T6(n)/C1) + (T15(n)/C3) + (5/C4)) / ((1/C1) + (1/C1) + (1/C3) + (1/C4)));
T6(n+1) = (((T5(n+1)/C1) + (T7(n)/C1) + (T16(n)/C3) + (5/C4)) / ((1/C1) + (1/C1) + (1/C3) + (1/C4)));
T7(n+1) = (((T6(n+1)/C1) + (T8(n)/C1) + (T17(n)/C3) + (5/C4)) / ((1/C1) + (1/C1) + (1/C3) + (1/C4)));
T8(n+1) = (((T7(n+1)/C1) + (T9(n)/C1) + (T18(n)/C3) + (5/C4)) / ((1/C1) + (1/C1) + (1/C3) + (1/C4)));
T9(n+1) = (((T8(n+1)/C1) + (T10(n)/C1) + (T19(n)/C3) + (5/C4)) / ((1/C1) + (1/C1) + (1/C3) + (1/C4)));
T10(n+1) = (((T9(n+1)/C1) + (100/C1) + (T20(n)/C3) + (5/C4)) / ((1/C1) + (1/C1) + (1/C3) + (1/C4)));

T12(n+1) = (((T11(n+1)/C3) + (T13(n)/C3) + (T22(n)/C3) + (T2(n+1)/C3)) / (4*(1/C3)));
T13(n+1) = (((T12(n+1)/C3) + (T14(n)/C3) + (T23(n)/C3) + (T3(n+1)/C3)) / (4*(1/C3)));
T14(n+1) = (((T13(n+1)/C3) + (T15(n)/C3) + (T24(n)/C3) + (T4(n+1)/C3)) / (4*(1/C3)));
T15(n+1) = (((T14(n+1)/C3) + (T16(n)/C3) + (T25(n)/C3) + (T5(n+1)/C3)) / (4*(1/C3)));
T16(n+1) = (((T15(n+1)/C3) + (T17(n)/C3) + (T26(n)/C3) + (T6(n+1)/C3)) / (4*(1/C3)));
T17(n+1) = (((T16(n+1)/C3) + (T18(n)/C3) + (T27(n)/C3) + (T7(n+1)/C3)) / (4*(1/C3)));
T18(n+1) = (((T17(n+1)/C3) + (T19(n)/C3) + (T28(n)/C3) + (T8(n+1)/C3)) / (4*(1/C3)));
T19(n+1) = (((T18(n+1)/C3) + (T20(n)/C3) + (T29(n)/C3) + (T9(n+1)/C3)) / (4*(1/C3)));
T20(n+1) = (((T19(n+1)/C3) + (100/C3) + (T30(n)/C3) + (T10(n+1)/C3)) / (4*(1/C3)));

T22(n+1) = (((T21/C3) + (T23(n)/C3) + (T12(n+1)/C3)) / (4*(1/C3)));
T23(n+1) = (((T22(n+1)/C3) + (T24(n)/C3) + (T13(n+1)/C3)) / (4*(1/C3)));
T24(n+1) = (((T23(n+1)/C3) + (T25(n)/C3) + (T14(n+1)/C3)) / (4*(1/C3)));
T25(n+1) = (((T24(n+1)/C3) + (T26(n)/C3) + (T15(n+1)/C3)) / (4*(1/C3)));
T26(n+1) = (((T25(n+1)/C3) + (T27(n)/C3) + (T16(n+1)/C3)) / (4*(1/C3)));
T27(n+1) = (((T26(n+1)/C3) + (T28(n)/C3) + (T17(n+1)/C3)) / (4*(1/C3)));
T28(n+1) = (((T27(n+1)/C3) + (T29(n)/C3) + (T18(n+1)/C3)) / (4*(1/C3)));
T29(n+1) = (((T28(n+1)/C3) + (T30(n)/C3) + (T19(n+1)/C3)) / (4*(1/C3)));
T30(n+1) = (((T29(n+1)/C3) + (100/C3) + (100/C3) + (T20(n+1)/C3)) / (4*(1/C3)));

end

T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
T13
T14
T15
T16
T17
T18
T19
T20
T21
T22
T23
T24
T25
T26
T27
T28
T29
T30

Can you guys please help me find where the problem is. Thank you

[John D'Errico]

Perhaps this should be a good lesson then? Teaching you not to create such huge lists of numbered variables? Instead, learn to use vectors and arrays.

Finding a bug in that code would make Cthulhu himself want to run screaming from the room.

[Elias Youwakim]

My project is to compute the temperatures for 30 nodes. So, I require this many equations.

[Stephen23]

"Can you guys please help me find where the problem is"

The problem is using lots of numbered variables, which forces you to write complex, buggy code. Instead, use vectors, matrices, and arrays. Then you can write less code. Less code is easier to follow and understand. Code that is easier to follow and understand is less buggy.

[Image Analyst]

Read this link first, then attach the full error message (ALL THE RED TEXT), not just a small snippet from it like you did.

[Elias Youwakim]

Sorry, I didn't know there were specifications on how to post the question. This is what I get: input a value for h: 25 input a value for k: 2.3 specify the number of iterations, n: 10 Index exceeds matrix dimensions. --> the only line in red.

Answer 1

[Walter Roberson]

Your code does not expand T11 or T21 as it runs but expects to be able to index them.

[Elias Youwakim]

Thank you for your help, it worked.