Matlab code wont disply the figure 2

c= 1; % unit conversion
L=1; % t=[L]/[c]
C=0.1; 
N=1000;
Np=N+1;
dx= L/N;
x=(0:dx:L)';
dt=C*dx/c;           
sqrC=C*C;
% step2 convert PDE to linear algebraic equations
A= sparse(Np,Np); % matrix creation as rows,columns
u= zeros(Np,1); % unknowns
b= zeros(Np,1); %RHS
% generate a wave function
u = sin(3*pi*x);
%figure(1);clf;hold on 
plot(x,u,'-b','Linewidth',L);
xlabel('x([L])')
ylabel('Amplitude([L])');
title('Intial Wave')
set(gca,'Linewidth',1,'fontsize',12)
box on;
ylim([-1,1]);

uset{1} = u; % future
uset{2} = u; % present
uset{3} = u; % previous
uset{4} = u; % previusly previous
% Apply boundary conditions
A(1,1)= 1; b(1)= 0;
A(Np,Np) = 1; b(Np) = 0;
for i= 2:Np-1
    A(i,i) =2 +sqrC*2;
    A(i,i-1) = -sqrC;
    A(i,i+1) = -sqrC;
    b(i) =5*uset{1}(i) - 4*uset{2}(i) + uset{3}(i);
end
%u=A/b
%uset{1}=u;
t=0;
Nt=100000;
for k=0:Nt
    t= t+dt;
    for i=2:Np-1
        b(i) =5*uset{1}(i) - 4*uset{2}(i) + uset{3}(i);
    end
    u=A\b;
    uset{3}=uset{2};
    uset{2}= uset{1};
    uset{1}=u;
end 
if k==1
    figure(2); clf; hold on;
    xlabel('x')
    ylabel('y','amplitude')
    set(gca,'Linewidth',1,'fontsize',12)
    box on
    h=1;
    ylim([-1,1])
end 
if mod(k,50)==0
    % figure(2);
    if h~=0; delete(h); end
    h = plot(x,u, '-b', 'Linewidth', 2);
    title(['Time:' num2str(t)]);
end 

Unrecognized function or variable 'h'.

Answer 1

[Walter Roberson]

h is not initialized so you cannot test

    if h~=0; delete(h); end

[Bijaya]

I have already defined h=1; BUT it still keep on giving same error . How do i fix it ?

[Dyuman Joshi]

No, that statement is subjected to a condition i.e. k==1. And as the condition is not satisfied (because the value of k is Nt), h=1 is not executed.

You can directly over-write h (if it has been defined), there's no need to delete it.