physics - Summing scalars and vectors [MATLAB] -

first off; i'm not taught in programming, tend learn need learn in order want when programming, have moderate experience python, html/css c , matlab. i've enrolled in physics-simulation course use matlab compute trajectory of 500 particles under influence of 5 force-fields of different magnitude.

so thing; need write following i=1...500 particles

f_i = m*g - sum{(f_k/r_k^2)*exp((||vec(x)_i - vec(p)_k||^2)/2*r_k^2)(vec(x)_i - vec(p)_k)}

i hope not cluttered

and here code far;

     clear     close     echo off
  
%simulation parameters-------------------------------------------
  
h = 0.01;                %time-step h (s) t_0 = 0;                %initial time (s) t_f = 3;                %final time (s) m = 1;                  %particle mass (kg) l = 5;                  %charateristic length (m) nt = t_f/h;             %number of time steps g = [0,-9.81];  f = [32 40 28 16 20];      %the force f_k (n) r = [0.3*l 0.2*l 0.4*l 0.5*l 0.3*l];    %the radii r_k p = [-0.2*l 0.8*l; -0.3*l -0.8*l; -0.6*l 0.1*l;                                            0.4*l 0.7*l; 0.8*l -0.3*l];                                           %forcefield origin position 
  
%stepper = 'forward_euler';          % use forward euler time-integration
  
fprintf('simulation parameters set');
  
%initialization---------------------------------------------------     = 1:500              %gives inital value each of 500     particles          particle{i,1}.x = [-l -l];
          particle{i,1}.v = [5,10];          particle{i,1}.m = m;   
           k = 1:5              c = particle{i}.x - p(k,:);              f = rdivide(f(1,k),r(1,k)^2).*c              %clear c;                %creates elements array f           end        particle{i}.fi = m*g - sum(f);     %compute attractive force on    particle       %clear f;                         %clear f next use       end 

what code seems goes first loop index i, goes through 'k'-loop , exits value f uses last value f(k) compute f_i. want put values of f(k) 1-5 , put matrix columns can sum f_i. i'd prefer sum columns first column should represent f-components in x-axis , second column f-components in y-axis.

note expression f in k-loop not done.

i fixed defining index f(k,:)