# 2D steady state heat conduction equation using Jacobi iteration

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Zahraa on 20 Sep 2020
Commented: Zahraa on 20 Sep 2020
2D steady heat conduction equation on the unit square subject to the following
Dirichlet boundary conditions:
T(x,0)=100x T(0,y)=200y
T(x,1) =200+100sin(pi*x) T(1,y)=100(1+y)
T(x,y) =0 (initial condition)
Use uniform grid in x and y of 21 points in each direction. Iterate until the maximum change is less than 0.1.
I set up the problem using a Jacobi iteration method;
and I have an issue setting up the boundary conditions correctly. Whenever I run the code it show me this (Unable to perform assignment because the size of the left side is 21-by-1 and the size of the right side is 21-by-21.) if any one could solve the issue for me? Thanks in advance !
Here's my code
for I=1:3
tic
% problem setup
Lx = 1; %length of x grid
Ly = Lx; % length of y grid
nx = 21; % number of nodes in x- direction
ny = nx; %number of nodes in y- direction
dx = Lx/(nx-1); % step size for spatial x-cord
dy = Ly/(ny-1); % step size for spatial y-cord
tol = 0.1; %error criteria
error = 9e9; %initialising error
k=0; %initialising iteration
% creating 1D and 2D grid
x = linspace(0,Lx,nx); %1d x grid
y = linspace(0,Ly,ny); %1d y grid
[x y] = meshgrid(x,y); %2d x-y grid
% initialising temperature array and BC
T = zeros(nx,ny); %initial condition array
% BC
T(1:ny,ny)= 100*(1+y) ;
T(1:ny,1)= 200*y ;
T(nx,1:nx)= 200+100*sin(pi*x) ;
T(1,1:nx)= 100*x ;
%creating a copy of temperature array after BC
Told = T;
while error > tol %while loop runs untill error > tolerance value
for i = 2:nx-1 %for loop runs for x values from 2 to last node -1
for j = 2:ny-1 %for loop runs for y value form 2 to last node -1
%iterative solver
if I== 1 %jacobi
figure(1)
T(i,j) = 0.25*(Told(i-1,j) + Told(i+1,j) + Told(i,j-1) + Told(i,j+1));
end
end
end
error_T = max(abs(Told - T)); %calculating error to decide wether while loop should stop or not
error = max(error_T); %calculating maximum error between absolute value of old arry T and new arry of T
Told = T; %updating temperature array for next iteration
k = k+1; %incrementing iterations by 1
% contour map
[C, h] = contourf(x,y,T); %contourf function used
clabel(C, h,'FontSize',8,'FontWeight','bold','color','k')
xlabel('spatial X -coordinate','FontSize',12)
ylabel('spatial Y -coordinate','FontSize',12)
title (sprintf('Temperature distribution on a %d x %d gridn using Jacobi method at iteration no %d', Lx, Ly, k),'FontSize',10)
pause(0.003)
end

John D'Errico on 20 Sep 2020
A picture may be worth a thousand words, but a picture of code is worthless, if you really want help. In fact, it is easier by far to paste in the code itself as simple text. That way someone can edit the code, and look far more easily at the code. Worse yet, you don't even show enough for someone to look at your specific problem.
Zahraa on 20 Sep 2020
thank you for your comment, I just edit it !

esat gulhan on 20 Sep 2020
T(1:ny,ny)= 200+100*(sin(pi*y(:,1))) ;
T(1:ny,1)= 200+100*y(:,1)
T(nx,1:nx)= 200*x(1,:) ;
T(1,1:nx)= 100*(1+x(1,:)) ;

#### 1 Comment

Zahraa on 20 Sep 2020
yes it works, thanks !