# while loop in a for loop

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Siti Jamilah Binti Mohd Yatim on 15 Apr 2021 at 11:51
Commented: Mathieu NOE on 19 Apr 2021 at 7:07
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
Mathieu NOE on 19 Apr 2021 at 7:07
tx for the reminder !
have a good day

Mathieu NOE on 19 Apr 2021 at 7:07
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

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