Exact solution Error in Heat Equation Matlab Code - matlab

Question

I wrote this code to solve one-dimensional heat transfer with dufort frankel method and want to compare with exact solution.
But exact solution gives an error. And when i run the code before the exact solution it is correct.
clc
clear
close all
%Declaration point..........................................................
nx=25; %number of point in the x direction
Ta=100; %temperatur (centigrade)
T=zeros(nx,1)+Ta; %initialization of temperator
T_in =0; %inlet temperature
T_out=0; %output temperature
Alpha=0.01; %coefficient (m^2/s)
L=1; %length (m)
x=linspace(0,L,nx); %x grid
dx=L/nx-1; %grid spacing
T(1)= T_in; %BC
T(nx)= T_out; %BC
dt=0.01; %time step from stability for DF
d=Alpha*dt/dx^2; %diffusion number
maxtime=10; %maximum time
nT=maxtime/dt; %time spacing
N=10; %number of series for exact computartion
%Time loop..................................................................
T0=T;
T1=T;
for n=1:nT
display(['Time step:',num2str(n),'time',num2str(n*dT)]);
T= DF(nx,T0,T1,d);
T0=T1;
T1=T;
end
%Exact solution............................................................
Ta = zeros(nx, nt);
for i=1:nx
for j = 1:nt
T(i,j) = sin(pi*x(i))*exp(-pi^2*t(j);
end
end
figure()
contourf(Ta,200,'linecolor','non')
%Error function............................................................
function [Err] = Error[T_exact,T,x];
Err=sqrt(sum(((T(2:end-1)-T_exact(2:end-1))./T_exact(2:end-1)).^2)/(N-2));
end