Line 36. Balancing the plot vectors. 'Error using plot Vectors must be the same length.'

T1=40;

T0=20;

a=10e-5;

L=0.1;

n=101; %No. of nodes

t=100;

dt=0.1;

time=0:dt:L;

dx=L/(n-1);

x=0:dx:L;

X0=T0*ones(n,1);

X0(1,1)=T1;

X(:,1)=X0;

d=ones(1,n);

for i=2:n-1

d(1,i)=2+(dx^2/(a*dt));

end

dd=-ones(1,n-1);

A=diag(d)+diag(dd,1)+diag(dd,-1);

A(1,2)=0;

A(n,n-1)=0;

for i=2:1+t/dt

b=(dx^2/(a*dt))*X0;

b(1,1)=T1;

b(n,1)=T0;

X(:,i)=inv(A)*b;

X0=X(:,i);

end

m=(n+1)/2;

figure();

plot (time,X(m,:),'Linewidth',3)

hold on

title('Transient temp distribution at center of the rod')

legend('Temp at the center of rod')

xlabel('Time,t(s)');

ylabel('Temperature,T(^oC)');

ylim([20 32])

Answer 1

[Walter Roberson]

for i=2:1+t/dt

t is 100 and dt is 0.1. You are expecting 100/0.1 to be exactly 1000. However 0.1 cannot be exactly represented in any finite length binary floating point representation, for exactly the same mathematical reason why 0.3333333.....3 can never exactly represent 1/3 in decimal no matter how many (finite) number of 3 you use. So 100/0.1 does not exactly equal an integer, and the : operator makes no attempt to round the number.