"Not enough input arguments" error

I keep getting the "Not enough input arguments" error in the following code and I was wondering if someone can help me fix?

function backward_heat(x,u0)
% Solves the heat equation by backward difference method and plots the 
% result; x - (pre-calculated) array of grid points
% in x, u0 - (pre-calculated) initial condition at grid points
N=length(x)-1;
if (N+1)~=length(u0)
    error('Dimensions of x and u0 must agree')
end
h=(x(N+1)-x(1))/N; 
tau=T/M; gamma=tau/h^2
w=zeros(N+1,M+1);
% grid points
t=(0:M)*tau;
% initial condition
w(:,1)=u0;
% solving the tridiagonal system by the double-sweep method
alpha=zeros(1,N);
beta=zeros(1,N);
for m=2:(M+1)
    for k=1:(N-1)
        alpha(k+1)=gamma/(1+gamma*(2-alpha(k)));
        beta(k+1)=(beta(k)*gamma+w(k+1,m-1))/(1+gamma*(2-alpha(k)));
    end
    for k=(N+1):(-1):3
        w(k-1,m)=alpha(k-1)*w(k,m)+beta(k-1);
    end
end
% surface plot of u(x,t)
w=w';
surf(x,t,w);

[Dyuman Joshi]

When you run the function, from where do you expect MATLAB to find the values for x and u0?

You need to supply the values when you call the function.

Also, the parameter M has not been defined as well.

[Josie]

My lecturer has provided this code as a solution to an assignment we did so all I'm trying to do is understand it. I am very new to MATLAB so I'm not yet able to effectively identify what's gone wrong.

Would you be able to explain what I need to do to get rid of the error please.

[Dyuman Joshi]

What is the assignment?

"Would you be able to explain what I need to do to get rid of the error please."

I did - You need to provide the values when you call the function. For your case, those would be x and u0.

Example - Let's take the tan function. You want to find the tan of something, but if you do not specify the value of something, how will MATLAB calculate the output?

So, it will give an error as follows -

tan

Error using tan
Not enough input arguments.

[Josie]

Ah ok I get it now thank you!

Answer 1

[Sulaymon Eshkabilov]

Variables T and M are also not specified. See how it can be executed:

x = 0:13;
u0 = ones(size(x));
backward_heat(x,u0)

gamma = 5

function backward_heat(x,u0)
% Solves the heat equation by backward difference method and plots the 
% result; x - (pre-calculated) array of grid points
% in x, u0 - (pre-calculated) initial condition at grid points
N=length(x)-1;
if (N+1)~=length(u0)
    error('Dimensions of x and u0 must agree')
end
h=(x(N+1)-x(1))/N; 
T = 10; M = 2;  % Some values are assigned for T and M
tau=T/M; gamma=tau/h^2
w=zeros(N+1,M+1);
% grid points
t=(0:M)*tau;
% initial condition
w(:,1)=u0;
% solving the tridiagonal system by the double-sweep method
alpha=zeros(1,N);
beta=zeros(1,N);
for m=2:(M+1)
    for k=1:(N-1)
        alpha(k+1)=gamma/(1+gamma*(2-alpha(k)));
        beta(k+1)=(beta(k)*gamma+w(k+1,m-1))/(1+gamma*(2-alpha(k)));
    end
    for k=(N+1):(-1):3
        w(k-1,m)=alpha(k-1)*w(k,m)+beta(k-1);
    end
end
% surface plot of u(x,t)
w=w';
surf(x,t,w);
end