I need to change the boundary condition in the code below

if true
  % code
% Heat diffusion in one dimensional wire within the explicit FTCS method
clear;
% Parameters to define the heat equation and the range in space and time
D = 1*10^-4;               % Heat Conductivity parameter in m2/s
K = 1*10^-4;               % Heat Conductivity parameter in s^-1
L = 5.;                    % Total length in m
T = 43200.;                   % Final Time
% Parameters needed to solve the equation within the explicit method
Nt = 7200;              % Number of time steps
Dt = T/Nt;              % Time step
Nx = 51;               % Number of space steps in m
Dx = L/(Nx-1);              % Space step
b = 1-(2*D*Dt/Dx^2)- K*Dt; % beta parameter in the finite- difference implementation
% Remember that the FTCS method is stable for b=<1
disp(b);
% The initial condition: the initial temperature of the pipe
for i = 1:Nx+1
      x(i) = (i-1)*Dx; % we also define vector x, due to the space discretization
      u(i,1) = sin (pi*x(i));
end
% Boundary conditions: the temperature of the pipe at the boundaries at any time
for k =1:Nt+1
    u(1,k) = 1.;  %% Edit: Lower BC at Temp = 1
    u(Nx+1,k) = 100.;   %% Edit: Upper BC at Temp = 100
    t(k) = (k-1)*Dt; % we also define vector t, due to the time discretization
end
% Implementation of the explicit FTCS method
for k =1:Nt             % Time Loop
  for i=2:Nx;         % Space Loop
      u(i,k+1) =u(i,k) + D*Dt/(Dx)^2*(u(i+1,k)-2*u(i,k)+u(i-1,k)); % Implementation of the FTCS Method
  end
end
%Graphical representation of the temperature at different selected times
figure(1)
plot(x,u(:,1),'-b',x,u(:,round(Nt/100)),'--g',x,u(:,round(Nt/10)),':b',x,u(:,Nt),'-.r')
title('Temperature of the pipe within the explicit FTCS method')
xlabel('X')
ylabel('T')
figure(2)
mesh(t,x,u)
% plot(t,u)
title('temperature of the pipe within the explicit FTCS method')
xlabel('t')
ylabel('x')

end