loop until condition met

im trying to create a loop until a certain condition exists by using the results at the end of each loop to calculate the next iteration. I've shown part of the code below. Iteration to terminate when Va = Vo = Vn.

Vo = [30 15 13 10];% initial V old to calc Re and f.
Va=zeros(size(Vo));
Vn=zeros(size(Vo));
%
while ~all([Va==Vo,Vo==Vn])
%
Re1 = (D(1).*Vo(1)) / nu;
%
Re2 = (D(2).*Vo(2)) / nu;
%
Re3 = (D(3).*Vo(3)) / nu; 
%
Re4 = (D(4).*Vo(4)) / nu;
%
A = [Matrix];
b = [Matrix];
Vn = A\b;% solves four unknowns at A\b
%
for i = 1:4
Va(i) = (alpha * Vn(i)) + ((1-alpha) * Vo(i));
Vo(i) = Va(i); %Used as Vo for each in next iteration.
end
end

Answer 1

[kjetil87]

Vo = [30 15 13 10];% initial V old to calc Re and f.

MaxIter=1e10;
%
Cntr=0;
while true
Cntr=Cntr+1;
%
Re1 = (D(1).*Vo(1)) / nu;
%
Re2 = (D(2).*Vo(2)) / nu;
%
Re3 = (D(3).*Vo(3)) / nu; 
%
Re4 = (D(4).*Vo(4)) / nu;
%
A = [Matrix];
b = [Matrix];
Vn = A\b;% solves four unknowns at A\b
%
for i = 1:4
Va(i) = (alpha * Vn(i)) + ((1-alpha) * Vo(i));
end

if all(abs(Va-Vn(1:4))<1e-10) && all(abs(Va-Vo)<1e-10) 
   break;
end
if Cntr==MaxIter  % add this to avoid being stuck if there is no solution.
   break;
end  

Vo=Va;

end

Answer 2

[kjetil87]

A while loop is what you are looking for it seems.

while ~all([Va==Vo,Vo==Vn])

      %your code

end

[kjetil87]

or maybe its more efficient with

while (Va~=Vo) && (Vo~=Vn)

end

[harley]

thanks i've edited the partial code above with your suggestion, i get an error, an suggestions?

??? Undefined function or method 'Va' for input arguments of type 'double'.
while ~all([Va(i)==Vo(i),Vo(i)==Vn(i)])

[harley]

thanks for your time, still getting similar error?

??? Undefined function or variable 'Va'.
while (Va~=Vo) && (Vo~=Vn)

[harley]

sorry i'm new to matlab, is that where you mean't, (see edited code above)

[kjetil87]

The error is because Va and Vn is not defined yet. Either pre define or use the answer below. Also note the different compare method used, because i doubt the 3 vectors will be EXACTLY equal so therefor it is better to compare using a threshold.