Changing a value in a while loop

Hey

I got great useful answers last time I asked so here I go again: As I run the code my value 'dt' doesn't change eventhough the condition 'if sum(F,j)-Fanvendt > 0.01*Fanvendt' is fulfilled - I've checked in the command window.

Thanks in advance.

%Debugging

clear clc %restarter alle kommandoer i Command window %alt køres ind med mm, N og MPa

% trinproces er 0,150 mm og stempeldiameteren er 110 mm

r = zeros(150,20); %preallocating = skrives for at lave hele matricen fra start, så det går hurtigere t = zeros(150,20); %; skrives for at matricen ikke skrives ud epsilontheta = zeros(150,20); epsilonn = zeros(150,20); epsilonr = zeros(150,20); den = zeros(150,20); det = zeros(150,20); der = zeros(150,20); epsilons = zeros(150,20); sigmas = zeros(150,20); sigman = 2*ones(150,20);%den første betingelse gør at sigman ikke må være 0 indledningsvis sigmar = zeros(150,20); k = zeros(150,20); l = zeros(150,20); A = zeros(150,20); F = zeros(150,20);

for i = 1:150 r0=110;%mm t0=1; %mm R=1.150; K=530; %N/mm^2 = MPa n=0.268; my=0.2;

    for j =1:20
        r(1,j)=r0-0.5*(j-1);
        r(i,1)=r0-1*(i-1);
    end

    %j = 1
    t(1,1)=t0;
    t(i,1)=t(1,1); 

    epsilonn(i,1)=0;
    epsilontheta(i,1)=0;
    epsilonr(i,1)=0;

    epsilons(i,1)=0;
    sigmas(i,1)=0;

    k(i,1)=0;
    l(i,1)=0;

    sigmar(i,1)=0;
    sigman(i,1)=0;
    F(i,1)=0;
end

    j=2;
    i = 1;
    processtop = 0;
    dt = 0;
    zonestop = 0;   
    processkift = 0;

while processkift == 0 %næste procestrin while processtop == 0 %kraftligevægtskriterie while zonestop == 0 %antal ringelementer i if j ~= 1 t(i,j)=t0+dt; %startantagelse af tykkelsen, dt ændrer sig if i ~=150 %tykkelsen i hvert procestrin er ens t(i+1,j)=t(i,j)+dt;

                    r(i+1, j) = sqrt((2*(r(i, j)^2*((t(i, j)+t(i+1, j))*(1/2))-(r(i, 1)^2-r(i+1, 1)^2)*t(i, 1)))/(t(i, j)+t(i+1, j)));
                end                        
                epsilonn(i,j)=log(t(i,j)/t0);  
                epsilontheta(i,j)=log(r(i,j)/r(i,1));
                epsilonr(i,j)= -(epsilonn(i,j) + epsilontheta(i,j));

                den(i,j)=epsilonn(i,j) - epsilonn(i,j-1);
                det(i,j)=epsilontheta(i,j) - epsilontheta(i,j-1);
                der(i,j)=-(den(i,j)+det(i,j));

                epsilons(i, j) = sqrt(R+1)*sqrt(R*(der(i,j)-det(i,j))^2+(der(i,j)-R*den(i,j))^2+(det(i, j)-R*den(i, j))^2)/(2*R+1);
                sigmas(i,j)= K*(epsilons(i,j))^n;

                k(i,j)= (sigmas(i,j)/epsilons(i,j))*((1+R)/(1+2*R))*(2*det(i,j)+den(i,j));
                %k=(sigmatheta(i,j)-sigmar(i,j))
                l(i,j)= (sigmas(i,j)/epsilons(i,j))*((1+R)/(1+2*R))*(den(i,j)*(1+R)+det(i,j)); %den(i,j) = 0
                %l=(sigman(i,j)-sigmar(i,j))

                sigmar(1,j) = 0;           
                if i ~= 150 %for sigmar = 2:150
                if j~=1 %er allerede defineret
                    sigmar(i+1, j) = (sigmar(i, j)+(1/2*(k(i+1, j)/r(i+1, j)+k(i, j)/r(i, j))+my*(l(i+1, j)+sigman(i, j))/t(i, j))*(r(i+1, j)-r(i, j)))/(1-my*(r(i+1, j)-r(i, j))/t(i, j));
                end
                end
            end

            if j == 1 % der er et loop inden i loopet
                sigman(i,1) = 0;
            else
                if i==1                    
                sigman(1,j)= l(1,j); %ved i=1 er sigmar = 0 
                else
                sigman(i,j)=l(i,j)+sigmar(i,j);
                end
            end
            if j ~= 1
            if sigman(i,j) >= 0
                zonestop = 1                
            else
                i = i + 1;
                zonestop = 0;                
            end 
            end
        end %while zonestop == 0

        if zonestop >= 1
            Fanvendt = 2.8*10^4; %N
            %if i ~= 150 %50 radier, men 49 ringelementer
            for i=1:i-1 %alle ringelementer frem til radius r(i,j)
                A(i,j)=((r(i,j))^2-(r(i+1,j))^2)*pi;
                F(i,j)= sqrt((sigman(i,j))^2)*A(i,j);              
            end              
            %end
            if sum(F(:,j)) - Fanvendt > 0.01*Fanvendt %istedet for numerisk tegn
                dt = dt + 0.01            
                zonestop = 0; %geninitialiserer zonestop
                processtop = 0;
                i = 1;  %starter forfra ved i = 1
            else   
                processtop = 1 
            end
        end % if zonestop >= 1
    end %while processtop == 0

    if processtop >= 1
        j = j+1
        %restarter alt undt. j
        zonestop = 0;
        processtop = 0;
        i = 1;
        dt = 0;
    end

    if j > 20
        processkift = 1 %terminerer alt
    end
end %while processkift = 0

[Jan]

And again I ask you for a proper code formatting. Please take the time to read the "Markup help" link on this page. Currently your code has a low readability only.

The TIC/TOC around single lines are still useless and increase the confusion level only.

We cannot run this code, because lines like "*dt = 0;*" are not valid. Such methods increase the difficulties to answer your question.

Answer 1

[Walter Roberson]

sum(F,j) is the sum of the array F along the j'th dimension. This will result in a row vector when j is 1, a column vector when j is 2, and a 2D array when j is 3 or more.

You then compare that vector or array against a constant. The result will be a logical vector or array. You then have an "if" test against that logical vector or array. MATLAB defines "if" of a vector or array to be considered true only if all the entries in the vector or array are non-zero (true).

My guess is that you want

if sum(F(:,j)) - Fanvendt > 0.01*Fanvendt

[Linda]

Good guess!

But do you then know why dt isn't added to all of the t's but only the two first? t for the same j should be the same? I have corrected the code above.

Answer 2

[Jan]

In the current form your code is very hard to debug. There are a lot of useless commands (TIC/TOC), the indentation is not clean, the comments are not in English, and including lines in stars prevents us from running your code.

Therefore I suggest to cleanup your code at first. An then set a breakpoint in the the line

if sum(F,j)-Fanvendt > 0.01*Fanvendt

and use the debugger to find the problem by your own. This is much more efficient than asking this forum.

[Linda]

I've cleaned the code and tried debugging. I placed a breakpoint at the 'if sum(F,j)-Fanvendt > 0.01*Fanvendt' and I triede going one step and the value of dt should change. And I wonder if it's because sum(F,j) isn't giving me what I want?

F is a matrix and I want Matlab to sum the j-array and subtract the value 28000 and then tell me if this is greater or smaller than 1% of 28000?