Save output data in a vector format while loop

Hi all,

I would like to export the output of the while loop in a vector format but it is not working for me... below is the code please advise.

Thanks

function [Q,h,t,v]= func (h0,D,d,dt)
g=9.81;
rho=1000;
h=h0; 
t=0; 
j=0;

% v=sqrt(2*g*h)

% h=(sqrt(h0)-1/2*d^2/D^2*sqrt(2*g)*t)^2
% Q=sqrt(2*g*h)*pi*d^2/2

while (t<228)
   j=j+1; 
   t=t+dt;
   h=((sqrt(h0))-((1/2)*(d^2)/(D^2)*(sqrt(2*g))*t))^2;
   v=sqrt(2*g*h);
   Q=sqrt(2*g*h)*pi*(d/2)^2;
   a(j)=Q;
   b(j)=h;
   c(j)=t;
   d(j)=v; 
end

Answer 1

[Geoff Hayes]

Ahmad - since your function signature defines the output parameters, then you can update these parameters rather than using them as "intermediaries" for the a, b, c, and d arrays. For example

function [Q,h,t,v]= func (h0,D,d,dt)
g = 9.81;
rho = 1000;
h = h0; 
t = dt:dt:228;  % create your t array with a step size of dt
Q = zeros(length(t), 1); % pre-allocate memory for your Q, h, and v arrays
h = zeros(length(t), 1);
v = zeros(length(t), 1);
for j = 1:length(t)
   h(j) = ((sqrt(h0))-((1/2)*(d^2)/(D^2)*(sqrt(2*g))*t(j)))^2;
   v(j) = sqrt(2*g*h(j));
   Q(j) = sqrt(2*g*h(j))*pi*(d/2)^2;
end

Try the above and see what happens!

[Ahmad Sayah]

Thanks Geoff,

still having an issue when calling out my function, i got "undefined function or variable 'ho' even though i have it defined with a value when i run my function, and it recognizes and error in my function as well...

can you please make the edits in the while loops?

Thanks!

[Geoff Hayes]

Ahmad - you may have a typo. Is the variable named ho or h0 (the letter 'o' vs the number 0)?

[Ahmad Sayah]

Thanks for the quick response!

but all are h0

[Geoff Hayes]

Please copy and paste the full error message to this question including the line number and code that is throwing the error.

[Ahmad Sayah]

here is the error:

Undefined function or variable 'h0'.

Error in hw4 (line 1)

[Q,h,t,v]= func (h0,D,d,dt)

[Geoff Hayes]

Ahmad - well if this is error is at line 1 of your hw4.m file then the error message makes sense since you haven't yet defined h0 (or D or d or dt). You need to define what these values should be or pass in numeric values into func.

[Ahmad Sayah]

Thanks so much!