How can I save the output in a loop to an external text file?

For my final project, I am measuring how the eccentricity of an orbit changes based on external forces introduced to the system

In my loop, I'm trying to save the outputted values of eccentricity to a text file so that I can use this to plot the answers for my results but it's just not working and I have no clue where I'm going wrong.

I don't want to save every value that comes out because there'll be a lot, I just want to save 1 value for every 100 so I've set up a for loop but I'm not very experienced with MATLAB so I think it's ended up a bit of a mess. Any help would be incredibly appreciated

The loop:

  D=dot(P(2,:), V(2,:))
  e1=norm(V(2,:));
  e1=e1^2
  mu=G*M(1)
  e2=e1/mu
  r1=norm(P(2,:))
  e3=e2/r1
  e4=e3*P(2,:)
  e5=D/mu
  e6=e5*V(2,:)
  e=e4-e6
  emag=norm(e)
  emag=emag/1.0e+10
      t = t + steps*delta;
      update_plot(P,H,t)
      
      m = 0;
      m = m + 1;
      if m == 100;
          i = 1:n
          C{i} = emag;
          C2{i} = t;
          
          E(i,1) = emag;
          E(i,2) = t;
          
          dlmwrite('local filename.txt',emag,'-append', '\t')
          dlmwrite('local filename.txt',t,'-append', '\t')
          m = 0;
     

      
      end
      
 end