How can I reverse a for loop?

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0 个投票

OK so i'm doing a quantum physics simulation with MATLAB. and part of this requires a for loop comparing position/velocity/acceleration against time. The full code can be found here https://github.com/crispyrolls93/Magnetic-Monopoles/blob/master/ForTest.m

The for loop in question is this:

 for n = (1:nmax)
    t = n * dt;
    V = (1/((t)^2))*(M + lamda * (1 - (1/sqrt(1 + (t^2/lamda))))^2);
    F = (V - E);
    a = F * x - v/t;
    v = v + a * dt;
    x = x + v * dt;    
    %Prints to output file
    fprintf(fxfid, '%18.18f \n', [x]');
    fprintf(fvfid, '%18.18f \n', [v]');
    fprintf(fafid, '%18.18f \n', [a]');
 end

This starts with an initial value of x and v and iterates through a number of time steps.

To test this I am trying to reverse the for loop, using the end point of the forward loop as the initial for the reverse loop. This is the reverse for loop:

 for n = (nmax:-1:1)
    t = n * dt;
    V = (1/((t)^2))*(M + lamda * (1 - (1/sqrt(1 + (t^2/lamda))))^2);
    F = (V - E);
    a = F * x - v/t;
    v = v + a * dt;
    x = x + v * dt;    
    %Display progress to terminal
    check = 10 * n / nmax;
    if any(check==A) == 1
           disp(100-10*check/4)
    end 
    %Prints to output files
    fprintf(fxrid, '%18.18f \n', [x]');
    fprintf(fvrid, '%18.18f \n', [v]');
    fprintf(farid, '%18.18f \n', [a]');
 end