Plot is zeroed out, how to fix this?

Hello,

I wrote a code that should give set values and plot them. For some reason i keep getting zero values. Any thoughts?

Now i am faced with a different problem. My plot comes out zeroed and i have no clue why. Any thoughts?

clc;
clear;
N=25;
% --Grid--
gridX = linspace(0,1,N);
gridT = linspace(0,0.5,N);
[x,t] = meshgrid(gridX,gridT);
A = linspace(0,1,N);
u = zeros(N,N);
xint = linspace(0,1,N);
%--Computation of An Terms--
n=1;
while n <= N;
    I(n) =  -(4*sin((pi*n)/2))/(pi*(n^2 - 4));
    A(n) = A(n) + I(n);
    n = n + 1;
end
while n <= N
    exponent = -(n.^2)*(pi.^2)*(t);  % n replaces lamda
    T = exp(exponent);
    X = A(n).*sin(n.*pi.*x);
    total = T*X;
    u(n) = u(n) + total;  %--Sum of all solutions--
    n = n + 1;
end
%--Plot--
figure;
surfc(x,t,u)
title('Project 2')
xlabel('X')
ylabel('Time')

Answer 1

[Mischa Kim]

Mike, after initializing u to zero you enter the first loop that increments n all the way to N. Which is why you never enter the second loop that is supposed to update u.

[Mike]

Well how would i go about changing that?

Lets just say i am not so good that this program at the moment.

Do i have to reassign an n value before before entering the second loop again?

[Mischa Kim]

Sorry about that. Yes, simply set n=1 right before entering the second loop.

Alternatively, you could try to combine the two loops. Any reason you kept them separate?

[Mike]

My lack of knowledge on loops is why they are seperate. I figured combining them would be better but i kept having issues when doing that.

[Mischa Kim]

Just looked at your code. Since I do not know what exactly you need to compute here are some thoughts:

• Change the corresponding command to: u = u + total. That way at least the dimensions work out.
• You are generating some huge numbers along the way so there are probably issues with some of the equations.