while loop in a for loop

hello. i am trying to plot a graph of ut (terminal velocity) against D (diameter) and my code is as below. i can plot the data but somehow the graph is not what i expected it to be. can someone help me? thank you in advance!

% m-file to plot ut vs D
D=0:1e-3:5e-3;
ut=miniclasstest1920_i(D);
plot(D,ut);
[D(1) ut(1)];
[D(end) ut(end)];
ut1=miniclasstest1920_i(1e-5);
ut2=miniclasstest1920_i(5e-3);
[ut1 ut2]

% function miniclasstest1920_i
function ut=f(D)
rho_s=2350;
rho=1100;mu=2e-3;
g=9.81;
LD=length(D);
ut=zeros(LD,1);
for n=1:LD
    u=zeros(10,1);
    Re=zeros(10,1);
    u(1)=1e-5;
    Re(1)=(rho*u(1).*D(n))/mu;
    err(1)=abs(Re(1)-0);
    i=1;
    while err(i)>1e-6
        if Re(i)<0.2
            u(i+1)=((g*D(n).^2)*(rho_s-rho))/(18*mu);
            Re(i+1)=(rho*u(i+1)*D(n))/mu;
        elseif 500<Re(i)<2e5
            u(i+1)=sqrt((3.*D(n)*g*(rho_s-rho))/rho);
            Re(i+1)=(rho*u(i+1)*D(n))/mu;
        else 
            disp('odd')
        end
        i=i+1;
        err(i)=abs(Re(i)-Re(i-1));
    end 
end
u=u(1:i-1);
ut(n)=u(end);
end
    

[Jan]

How can we help you based on the information "somehow the graph is not what i expected it to be"? We do not know, what you expect.

[Mathieu NOE]

hello

code fixed !! the output of the function was incorrect (wrong index and not at the right position in the loop structure)

% m-file to plot ut vs D
D=0:1e-3:5e-3;
ut=f(D);
plot(D,ut);

function ut=f(D)
rho_s=2350;
rho=1100;
mu=2e-3;
g=9.81;
LD=length(D);
ut=zeros(LD,1);
for n=1:LD
    u=zeros(10,1);
    Re=zeros(10,1);
    u(1)=1e-5;
    Re(1)=(rho*u(1).*D(n))/mu;
    err(1)=abs(Re(1)-0);
    ci=1;
    while err(ci)>1e-6
        if Re(ci)<0.2
            u(ci+1)=((g*D(n).^2)*(rho_s-rho))/(18*mu);
            Re(ci+1)=(rho*u(ci+1)*D(n))/mu;
        elseif 500<Re(ci)<2e5
            u(ci+1)=sqrt((3.*D(n)*g*(rho_s-rho))/rho);
            Re(ci+1)=(rho*u(ci+1)*D(n))/mu;
        else 
            disp('odd')
            ci
        end
        ci=ci+1;
        err(ci)=abs(Re(ci)-Re(ci-1));
    end 
    ut(n)=u(ci) ; % and not u(end)
end
end

[Siti Jamilah Binti Mohd Yatim]

thank you Mathieu NOE for fixing my code!

[Mathieu NOE]

Glad I could help

have a good day

[Jan]

@Mathieu NOE: If you post this as an answer, it can be accepted.

[Mathieu NOE]

@Jan

tx for the reminder !

have a good day

Answer 1

[Mathieu NOE]

hello again

official answer below :

code fixed !! the output of the function was incorrect (wrong index and not at the right position in the loop structure)

% m-file to plot ut vs D
D=0:1e-3:5e-3;
ut=f(D);
plot(D,ut);
function ut=f(D)
rho_s=2350;
rho=1100;
mu=2e-3;
g=9.81;
LD=length(D);
ut=zeros(LD,1);
for n=1:LD
    u=zeros(10,1);
    Re=zeros(10,1);
    u(1)=1e-5;
    Re(1)=(rho*u(1).*D(n))/mu;
    err(1)=abs(Re(1)-0);
    ci=1;
    while err(ci)>1e-6
        if Re(ci)<0.2
            u(ci+1)=((g*D(n).^2)*(rho_s-rho))/(18*mu);
            Re(ci+1)=(rho*u(ci+1)*D(n))/mu;
        elseif 500<Re(ci)<2e5
            u(ci+1)=sqrt((3.*D(n)*g*(rho_s-rho))/rho);
            Re(ci+1)=(rho*u(ci+1)*D(n))/mu;
        else 
            disp('odd')
            ci
        end
        ci=ci+1;
        err(ci)=abs(Re(ci)-Re(ci-1));
    end 
    ut(n)=u(ci) ; % and not u(end)
end
end