iterations while in loop

harley (view profile)

on 27 Aug 2013
Accepted Answer by Jan Simon

Jan Simon (view profile)

having trouble making this iterate for each increment of Vn, it goes straight to Vn = 30, i want it to also to calc a new Re, f, dPloss_1, Va & Q with each new iteration.

```D = 0.1; L = 10;
A = 0.25*pi*D^2;
e = 0.0015e-3;
rho = 998;
nu = 1.01e-6;
eoverD = e/D;
alpha = 0.1;
Vo = 2;
for Vn = 2:0.1:30;% iteration length.
%
Re = (Vo.*D) / nu;
%
if Re < 2300
f = 64 / Re;
else
darbyFormula = @(x) 1/sqrt(x)+2*log10(eoverD/3.7 + 2.51/Re/sqrt(x));
f = fzero(darbyFormula,0.01);
end
%
dPloss_1 = (f*rho*(L/D)) * ((Vn*Vo)./2);
Va = (alpha*Vn)+((1-alpha)*Vo);
Q=Va*A;
Vo = Va;
end %
```

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harley

harley (view profile)

on 27 Aug 2013

code edited, yes i want it to update at each iteration saving previous values of Re, f, dPloss_1, Va and Q etc.

David Sanchez

David Sanchez (view profile)

on 27 Aug 2013

but what is the problem?

harley

harley (view profile)

on 27 Aug 2013

David actually works fine, sorry for the confusion.

Jan Simon (view profile)

Answer by Jan Simon

Jan Simon (view profile)

on 27 Aug 2013

No, of course it iterates through 2:0.1:30. You can test this easily either by using the debugger or by a disp(Vn) command inside the loop.

The problem might be, that the result is overwritten in each iteration. So try:

```Vn_pool = 2:0.1:30;
Q = zeros(1, length(Vn_pool)));  % pre-allocate!!!
for k = 1:length(Vn_pool)
Vn = Vn_pool(k);
...
Q(k) = Va * A;  % same for the other values wanted as outputs
end
```

harley

harley (view profile)

on 27 Aug 2013

yes your right, its over writing each iteration, thanks.