# What is wrong in code of diffusion equation problem?

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a=4; b=4; na=20; nb=16; k=5; to=80;
clear T
x=linspace(0,a,na);
y=linspace(0,b,nb);
[X,Y]=meshgrid(x,y);
for i=1:nb
for j=1:na
T(i,j)=0;
For n=1:k
Ns=2*n-1;
T(i,j)=T(i,j)+sin(ns*pi*X(i,j)/a).*sinh(ns*pi*Y(i,j)/a)/(sinh(ns*pi*b/a)*ns);
End
T(i,j)=T(i,j)*4*To/pi;
End
End
Mesh(X,Y,T)
Xlabel(x (m));ylabel(y (m));zlabel(T(^oC))

Walter Roberson on 18 Sep 2016
First of all you need to use for and end not For and End -- MATLAB is case sensitive.
Xlabel(x (m));ylabel(y (m));zlabel(T(^oC))
uses Unicode Character 'LEFT SINGLE QUOTATION MARK' (U+2018) and Unicode Character 'RIGHT SINGLE QUOTATION MARK' (U+2019) instead of apostrophe. U+2018 and U+2019 are also known as "smart quotes" because some editors automatically change apostrophes around words to these quotes because those quotes are used in publishing and writing text (but seldom in computer code.)
Attila Monteiro de Abreu on 18 Sep 2016
Thank you so much brother!!! You help me in my work of conclusion of course in Engenering Mechanical! I'm really greatfull!!

Byron Castillo on 22 Jan 2021
a=5; b=4; na=20; nb=16; k=5; T0=80;
clear T
x=linspace(0,a,na);
y=linspace(0,b,nb);
[X,Y]=meshgrid(x,y);
for i=1:nb
for j=1:na
T(i,j)=0;
for n=1:k
ns=2*n-1;
T(i,j)=T(i,j)+sin(ns*pi*X(i,j)/a).*sinh(ns*pi*Y(i,j)/
a)/(sinh(ns*pi*b/a)*ns);
end
T(i,j) = T(i,j)*4*T0/pi;
end
end
mesh(X,Y,T)
xlabel('x (m)'); ylabel('y (m)'); zlabel('T ( ^oC)')