Can someone please check my code and tell me what is the issue with it?

Can someone please correct my code? I have been trying this code since sometime but I do not understand the issue with my code. If someone can tell me what went wrong with my code, it would be greatly appreciated. I have attached the question and my solution below. This is taken from a learning lab, and the blocks in grey are unable to be manipulated. I am attaching the question with my solution just in case someone has any doubts. I have also attached the error which I keep on getting when I am trying to submit my code.

%function omega = flow_around_cylinder_unsteady
Re=60;
%%%%% define the grid %%%%%
n=101; m=202; % number of grid points
N=n-1; M=m-2; % number of grid intervals: 2 ghost points, theta=-h,2*pi
h=2*pi/M; % grid spacing based on theta variable
xi=(0:N)*h; theta=(-1:M)*h; % xi and theta variables on the grid
%%%%% time-stepping parameters %%%%%
t_start=0; t_end=0.5; %vortex street starts at around t=1000
tspan=[t_start t_end]; 
%%%%% Initialize vorticity field %%%%%
omega=zeros(n,m);
%%%%% Construct the matrix A for psi equation %%%%%
boundary_index_bottom = 1:n;
boundary_index_left = 1:n:1+(m-1)*n; 
boundary_index_top= 1+(m-1)*n:m*n;
boundary_index_right = n:n:m*n;
diagonals1 = [4*ones(m*n, 1), -1*ones(m*n, 4)]; 
A=spdiags(diagonals1, [0 -1 1 -n n], m*n, m*n); %interior points
I=speye (m*n);
A(boundary_index_left, :)=I (boundary_index_left,:); 
A(boundary_index_right, :)=I (boundary_index_right, :); 
diagonals2 = [ones(m*n,1), -1*ones(m*n, 2)];
Aux = spdiags (diagonals2, [0 m* (n-1) -m* (n-1)], m*n, m*n); 
A(boundary_index_top, :)=Aux (boundary_index_top, :); 
A(boundary_index_bottom, :)=Aux (boundary_index_bottom, :);
%%%%% Find the LU decomposition %%%%%
[L,U]=lu(A); clear A;
%%%%% Compute any time-independent constants %%%%%
%%%%% advance solution using ode23 %%%%%
options=odeset('RelTol', 1.e-03);
omega=omega(2:n-1,2:m-1); % strip boundary values for ode23
omega=omega(:); % make a column vector
[t,omega]=ode23...
  (@(t,omega)omega_eq(omega,L,U,theta,xi,h,Re,n,m), tspan, omega, options);
%%%%% expand omega to include boundaries %%%%%
temp=zeros(n,m);
temp(2:n-1,2:m-1)=reshape(omega(end,:),n-2,m-2);
omega=temp; clear temp;
%%%%% compute stream function (needed for omega boundary values) %%%%%
omega_tilde = zeros(n,m); 
omega_tilde (1,:)=0;
omega_tilde (n,:)=exp(xi (n))*sin(theta); 
omega_tilde(:,1)=0; 
omega_tilde(:,m)=0;
for i=2:n-1
   for j=2:m-1
       omega_tilde(i,j) = h^2*exp(2*xi(i))*omega(i,j);%interior points
   end
end
omega_tilde = omega_tilde(:);
psi = reshape(U\(L\omega_tilde), n, m);
%%%%% set omega boundary conditions %%%%%
omega(1,:)= (psi(3,:) - 8*psi(2,:)) * 1/(2*h^2);
omega(n, :)=0;
omega (:,1)=omega (:,m-1);
omega(:,m)=omega (:,2);
%%%%% plot scalar vorticity field %%%%%
plot_Re60(omega,t_end);

Unrecognized function or variable 'plot_Re60'.

%end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function d_omega_dt=omega_eq(omega,L,U,theta,xi,h,Re,n,m)
%%%%% expand omega to include boundary points %%%%%
temp=zeros(n,m);
index1=2:n-1; index2=2:m-1;
temp(index1,index2)=reshape(omega,n-2,m-2);
omega=temp; clear temp;
%%%%% compute stream function %%%%%
omega_tilde = zeros(n,m); 
omega_tilde (1,:)=0;
omega_tilde (n,:)=exp(xi (n))*sin(theta);
omega_tilde(:,1)=0; 
omega_tilde(:,m)=0;
for i=2:n-1
for j=2:m-1
omega_tilde(i,j) = h^2*exp(2*xi (i))*omega (i,j); %interior
   end 
end 
omega_tilde = omega_tilde(:);
psi = reshape(U\(L\omega_tilde), n, m);
%%%%% compute derivatives of omega %%%%%
omega (1,:)= (psi(3,:) - 8*psi(2,:)) *1/(2*h^2); 
omega(n, :)=0;
omega(:,1) =omega(:,m-1); 
omega(:,m)=omega(:,2); 
d_omega_dt=zeros(n-2,m-2);
for i=2:n-1
  for j=2:m-1
   d_omega_dt (i-1,j-1)=...
2*exp(-2*xi(i))* 1/(h^2*Re)*...
(omega(i+1,j)+omega(i-1, j)+...
omega(i, j+1)+omega(i, j-1)-4* omega(i,j))... 
+exp(-2*xi (i))/(4*h^2)*...
((psi(i+1, j)-psi (i-1, j))*(omega(i, j+1) -omega(i, j-1))-... 
(psi(i, j+1)-psi(i,j-1))*(omega(i+1, j)-omega(i-1,j)));
  end
end
d_omega_dt = d_omega_dt(:);
end

[KSSV]

Attaching code as an image wont help us to help you. Copy and paste your code here so that we can copy it and run it.

[Aisha Singhania]

Okay. Can you please check now?

[Torsten]

Code works, but you forgot to include the plot routine (see above).

[Aisha Singhania]

Can you please tell me how to add it? I am still getting error when I'm clicking on submit. I tried to add the plot routine, but it still shows invalid. Your answer will be much appreciated. Thank you.

[Cris LaPierre]

The code you have shared does not produce the error in line 18 that you are getting. We are missing something, but it's impossible for us to say what.

Where this is a MATLAB Grader assignment, please consider asking your instructor.

This appears to be one of the final assignments in Mathematics for Engineers: The Capstone Course on Coursera

Answer 1

[Cris LaPierre]

The issue is due to a combination of things: leaving a space between a function name and its inputs combined with building an array using square brackets.

The extra space is causing MATLAB to treat the function name and its inputs as 2 separate matrix elements.

% Works on its own
ones (5,1)

ans = 5×1

1 1 1 1 1

% This syntax must be used when building an array
[ones(5,1)]

ans = 5×1

1 1 1 1 1

% Your syntax causes an error when used inside square brackets
[ones (5,1)]

Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

The fix, then, is to have the input arguments immediately follow the function name. Remove all spaces between ones and the corresponding input arguments (...)

[Cris LaPierre]

Just a note that I had to go back to your screenshots to find the error, since the code you pasted is different (doesn't have the offending space). In the future, please share the actual code that is creating the error.

[Aisha Singhania]

Okay. Thank you so much, I'll fix the issue.