help plotting at x=0 dt/dx=0

This is the code the pipe that i am coding and is insulated and i need to incorporate that at x=0 dt/dx=0 but i am having trouble where to put it and how to put it

my graph is suppose to be flipped doing the at x=0 dt/dx=0

clear all

close all

Tinf=300;

Tb=400;

n=25;

L=1; %m

nsquare=25; %/m^2

dx=L/n;

aw=1/dx;

ae=aw;

ap=aw+ae+nsquare*dx;

A=zeros(n,n);

b=zeros(n,1);

for i=2:n-1 % number of equations

A(i,i)=ap; %Ap

A(i,i-1)=-aw; %Aw

A(i,i+1)=-ae; %Ae

b(i)=nsquare*dx*Tinf;

end

i=1

A(i,i)=3/dx+nsquare*dx; %Ap

A(i,i+1)=-1/dx; %Ae

b(i)=2*Tb/dx+nsquare*dx*Tinf;

i=n

A(i,i)=1/dx+nsquare*dx; %Ap

A(i,i-1)=-1/dx; %Aw

b(i)=nsquare*dx*Tinf;

T=linsolve(A,b)

hold on

figure(1)

plot(T)

title('Phi as function of grid point')

axis([0 n 0 100])

xlabel('i') % x-axis label

ylabel('Phi') % y-axis label

T_BC=zeros(n+2,1);

T_BC(1)=Tb;

for i=2:n+1 % number of equations

T_BC(i)=T(i-1);

end

T_BC(n+2)=T_BC(n+1);

y(1)=0;

y(2)=dx/2;

y(n+1)=L-dx/2;

y(n+2)=L;

for i=3:n % number of equations

y(i)=y(i-1)+dx;

end

figure(2)

plot(y,T_BC)

title('Phi as function of x')

xlabel('x') % x-axis label

ylabel('T') % y-axis label

Answer 1

[Ashish Mishra]

The condition, dt/dx=0, is already included in the code because it implies that at that given x ,T(i)=T(i-1) and flip function can be used to flip the T matrix , so that the plot of T will be flipped.

https://www.mathworks.com/help/matlab/ref/flip.html