For loop does not change values of matrix

Question

Jort Puiman 2023-7-31

0
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https://ww2.mathworks.cn/matlabcentral/answers/2002607-for-loop-does-not-change-values-of-matrix

编辑： Dyuman Joshi 2023-7-31

Hi everyone,

I want to model the concentration gradient in a centrifuge over distance and time. However, I am struggling getting the wall description to work. I divided the centrifuge in cells, and I want to fill each cell at the wall until a certain concentration cmax is reached. Then, I want to place the excess in a previous cell. For this, I made a for-loop that uses the precalculated concentration, and reassesses every cell from the wall to the center. When running the code, I see that the for-loop does not change anything. Could anyone help me with this problem and explain to me why the for-loop does not change anything? Below the function, also I inserted the files I use.

function [dcdt] = odepaper(t, c, Nr,  dr, vgs, cmax,cini,n)
dcdt=zeros(Nr,1);
r = zeros(Nr,1);
v = zeros(Nr,1);
excess= zeros(Nr,1);
%% Loop
for i=2:Nr
   r(i) = r(i-1)+dr;
   v(i) = (1-c(i))^n*vgs;
   vin = (1-cini)^n*vgs;
   rin = 0.5*dr;
       if i == 1        % Initial conditions
            dcdt(1)=(1/dr)*((rin*cini*vin)/r(i)-c(i)*v(i));
       elseif i == Nr   % Wall conditions
           dcdt(Nr) = (1/dr)*((r(i-1)*c(i-1)*v(i-1))/r(i))+excess(i);
       else             % Everything in between
           dcdt(i) = (1/dr)*((r(i-1)*c(i-1)*v(i-1))/r(i)-c(i)*v(i))+excess(i);
       end
end
%% Mass replacement
for i = Nr:-1:2         % Force system to give back excess to previous cells
    c(i) = c(i)+excess(i);
    if c(i)>cmax
    excess(i) = c(i)-cmax;
    c(i) = cmax;
    c(i-1) = c(i-1)+excess(i);
    end
end
end