Must be a positive integer or logical

Im having trouble with this code I need to the matrix to go up in steps of either 0.0052 for the time or to complete the loop t<t_2 in steps of 0.0052 or 1:(t_2/del_t).

      %Aluminium Material Properties%
      clear all
      close all
      clc
      rho =   2700  ;   %kg/m^3 Density
      k   =   170   ;   % 
      cp  =   910   ;   %

      alpha = k/(rho*cp); %
      L_d     =   0.0047;                 %m  Diameter
      L_x     =   0.047;                  %m  Length in x direction
      L_r     =   L_d/2;                  %m  Radius
      n_r     =   2;                      %   Nodes in r direction
      n_x     =   40;                     %   Nodes in x direction
      del_x   =   L_x/(n_x-1);             %m  Spacing of Nodes
      T_h     =   27;                     %C  Temperature of Hot Side
      T_i     =   19;                     %C  Initial Temperature
      t_2     =   180;                    %s  Simulation Time
      t(1)    =   0;                      %s  Initial Time
      Fo_1      =   0.25;                   %   Fourier Number Stability 0.25 For 3D
      del_t   =   (Fo_1*del_x^2)/alpha;      %   Calculate time step using Fourier Number for Stability
      h       =   5;
      %Set Inital Matrices Temp
      T(1:n_r+2,1:n_x+2,1) =  T_i;      %Sets matrix dimensions and sets it to 19 C

      Fo                      = alpha*del_t/(del_x.^2)                            ; %        Fourier Number
      Bi                      = h*del_x/k                                       ;  %     Biot Number

      if Fo > 0.25
          fprintf('Fo Number to big, code unstable \n \n')  %Check if Fo is acceptable
      elseif Fo*(1-Bi) > 0.25
          fprintf('Bi Number to big, code unstable')         %Check if Bi is acceptable
      end

      k = 1;

      while t<t_2                        %   Time Loop

          for r=1:n_r+2                     %   Space Loop r direction

               for x=1:n_x+2                 %   Space Loop x direction

                   if x==1 || x==42 || r==1 || r==4   % Sets Boundary Conditions for Room Temp 

                       T(r,x,k+1) = 19; 

                    elseif x==2                %   Boundary Condition First Node = 27 Celius                %   Boundary Condition First Node = 27 Celius

                        T(r,x,k+1) = 27;       

                  elseif x>2 || x==n_x  %   Middle to End of Material 

                      T(r,x,k+1) = alpha*del_t*(((T(r,x+1,k)-(2*T(r,x,k))+T(r,x-1,k))/L_x^2)+((T(r+1,x,k)-(2*T(r,x,k))+T(r-1,x,k))/L_r^2))+T(r,x,k);  %Using finite difference method

                  end
              end
          end

      t(k)  =   k+del_t; %Sets time
      k       =   k+del_t;

      end

      Temp(1:n_r,1:n_x)   =   T(1:n_r,1:n_x,k);

This is the error that I am receiving

??? Attempted to access T(1,1,2.00525); index must be a positive integer or logical.

Error in ==> Transient2D at 37
                 T(r,x,k+1) = 19;

[per isakson]

Please do not dumb such a lot of poorly formatted and irrelevant code here.

[Luke Cartwright]

What is irrelevant?

[per isakson]

everything before k = 1; for a start.

If you want us to run the code say so and provide the code as an attachment.

Answer 1

[per isakson]

Use the debug support. It's good. Here are some links on debugging in Matlab

• Debugging in MATLAB
• Debugging session
• Debugging Approaches

Find out why k is not a whole number.

k = k+del_t; is the prime suspect.

[Luke Cartwright]

well k is the time step so

k+del_t - 1+0.0052

If I changed it to

k=k+1

Then it will only run for 181 cycles when it needs run for t_2/del_t = 34615 approx.

[per isakson]

Maybe it is not appropriate to use k as an index. You must make sure k is a whole number.