I want to create an if loop inside multiple if loops that are already present

I want to stop a piece of code once a certain variable goes past a certain number.

I am not sure exactly where to put it but essentially I want the code to stop once Vr is < arbitrary number, 0.004, let us say

       if Vf_new < Vr(3,1) && delta_Vfc >= 1E-6
            %
            disp('update')
            Vr(3,1) = Vf_new;
            iter = iter + 1;
            %
        elseif delta_Vfc < 1E-6 || Vf_new <= Vr(3,1)
            %
            disp('do not update')
            continue_iteration = 0;
            %
        end    

It wants to appear here.

I am just not sure how to nest it inside an already existent if elif loop. I think it should look like this...

        if Vf_new < 0.004
            return
        end

Help please

Thanks

Alex

Answer 1

[Image Analyst]

Not sure what you have: a for loop or multiple if/else blocks. An "if" block is not called a loop because it does not loop/iterate.

Let's say that you have a for loop and inside the for loop is your if tests and you want to check Vf_new at the beginning of the loop

for k = 1 : 10000
    if Vf_new < 0.004
        break; % Breaks out of the for loop and continues the program after the for loop.
        % OR you can exit the loop and the entire function or program you're
        % in by calling return;
        % return; % Step out of the entire program.
    elseif Vf_new < Vr(3,1) && delta_Vfc >= 1E-6
        fprintf('Updating.  Now Vf_new = %f.\n', Vf_new);
        Vr(3,1) = Vf_new;
        iter = iter + 1; % If iter is your for loop variable, then you don't need this line.  If it's a while loop you may need this or something like it.
    elseif delta_Vfc < 1E-6 || Vf_new <= Vr(3,1)
        fprintf('NOT updating.  Now Vf_new = %f.\n', Vf_new);
        continue_iteration = 0; % If your loop is a for loop, then you don't need this line.  If it's a while loop you may need this or something like it.
        break; % Get out of loop.  Do not continue iterating.
    end    
end

[A Poyser]

It is quite a long for loop so I only added what I thought was important for brevity, I will add a little more for context.

N = 1000;
% 
% materials properties and preset variables goes here
% 
for k = 1:N
    %
    k;
    %
    sigma_infty(:,k) = [10*k 0 0 0 0 0]'; % far-field stress
    %
    %
    % Crack density parameter (from Budiansky and O'Connel, IJSS 12:81-97,
    % 1976) in composite
    cdp = 0.05; % 
    Vcc = 4/3*pi*cdp*a3_over_a1; % compute volumetric density of cracks in composite
    %
    if k == 1
        Vr(3,1) = Vfc; % volume fraction of fibres
    else
        Vr(3,1) = Vfc*exp(-(sigma_f(1,k-1)/sYW)^mW); % volume fraction of the fibres corrected for failure based on the previous iteration
    end
    delta_Vfc = 1E6;
    iter = 1;
    continue_iteration = 1;
    %
    while continue_iteration && iter < 10
        %
        % some maths to calculate mechanical properties goes here...
        %
        Vf_new = Vfc*exp(-(sigma_f(1,k)/sYW)^mW);
        delta_Vfc = abs(Vf_new-Vr(3,1));
        %
        if Vf_new < Vr(3,1) && delta_Vfc >= 1E-6
            %
            disp('update')
            Vr(3,1) = Vf_new;
            iter = iter + 1;
            %
        elseif delta_Vfc < 1E-6 || Vf_new <= Vr(3,1)
            %
            disp('do not update')
            continue_iteration = 0;
            %
        end    
        %
    end
end
% 

I tried adding the piece of code that you suggested but it didn't seem to be able to break the loop.

Thanks

Alex