how to use 'optim.pro​blemdef.Op​timization​Variable' as double

this is the code:

%cost rates
P = 20

P = 20

    H = 0.1 *P

H = 2

    B = 10*P

B = 200

    E = P;
%demand vector
D = [21    37     1    16     8     5    10    18    20    27    21    35    11    44     2    34    21    28     8    10    41    49    16    35    44    45     5     2     9    44     5    22    48    27    35    16    35    42     1    38    50    38    15    40     6    23    46    15    15     7]

D = 1×50

21 37 1 16 8 5 10 18 20 27 21 35 11 44 2 34 21 28 8 10 41 49 16 35 44 45 5 2 9 44

%shelf life
L = 4

L = 4

 % Initialize variables
    T = length(D);  % Number of days
    I = zeros(1, T);  % Inventory levels
    order_qty = zeros(1, T);  % Order quantities
    Sexpired = zeros(1, T); % Expired quantities
       A = zeros(1, T); % age of inventory
       C = zeros(1,T); % backorder amount per day
       in = zeros(1,T); % leftover inventory per day
       max_inventory = 50;
    % Initial conditions
   I(1,1) = 10;
     A(1,1) = 0;
    % starting loop
     for t = 1:T-1

      % calculate leftover inventory
      in(t) = max(0,(I(t)-D(t)));
      if in(t) == 0
          %order_qty(t) = max(0, max_inventory - I(t)); %order upto S
%%%%%%%%%%%%%%% getting error in this line%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
          order_qty(t) = X; % assigning value of optimised variable to order_qty for today
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%        
          C(t) = abs(I(t)-D(t)); % counting backorders or shortage
          A(t+1) = 1; % Reset age to 1 when new inventory arrives
          I(t+1) = min(max_inventory, order_qty(t)); % inventory level for tomorow
         else 
    % FIFO implementation
        A(t+1) = A(t) + 1; % Increase age for existing items
        A(t+1) = min(A(t+1), L); % Cap age to L
    % Check for expired items
          if A(t+1) >= L % if expired i.e age exceeds shelf life
             Sexpired(t) =  in(t); % count leftover inventory today as expired and discard
             A(t+1) = 1; % Reset age to 1 for the newly ordered items tomorow
             I(t+1) = min(max_inventory,order_qty(t)); % tomorow inventory will be only new arrival

          end
      end
    end

Unrecognized function or variable 'X'.

% Calculate costs
 holding_cost = sum(H .* I);
purchase_cost = sum(P .* order_qty);
expiry_cost = sum(E .* Sexpired);
shortage_cost = sum(B .* C);
    % Calculate total cost outside the loop
    total_cost = holding_cost + purchase_cost + expiry_cost + shortage_cost;
    % Display costs
    disp(['Holding Cost: ' num2str(holding_cost)]);
    disp(['Purchase Cost: ' num2str(purchase_cost)]);
    disp(['Expiry Cost: ' num2str(expiry_cost)]);
    disp(['Shortage Cost: ' num2str(shortage_cost)]);
    disp(['Total Cost: ' num2str(total_cost)]);
% Display quantity ordered each day
    disp('Quantity Ordered Each Day:');
    disp(order_qty);
    disp(Sexpired);
% Create optimization variables
X3 = optimvar("X","LowerBound",0,"UpperBound",50);

% Set initial starting point for the solver
initialPoint4.X = repmat(25,size(X3));

% Create problem
problem = optimproblem;

% Define problem objective
problem.Objective = sum(H * I + B * C + E * Sexpired + P * order_qty);

% Set nondefault solver options
options = optimoptions("ga","CreationFcn","gacreationlinearfeasible");

% Display problem information
show(problem);

% Clear variables
clearvars X3 initialPoint4 options

[Torsten]

You use the variable X

order_qty(t) = X; % assigning value of optimised variable to order_qty for today

before you define it

X3 = optimvar("X","LowerBound",0,"UpperBound",50);

But this is not the only problem with your code.

[Gauri]

Can you please guide me to remove the errors

[Torsten]

We need a mathematical description of your optimization problem.