creating a loop and functions

Hi,

I'm trying to perform a simple model but can't seem to create a loop. The issue is that I use known values (ho and hl) to solve the equation.

Then I need to use a data set of (ho) consisting of a column of 298 into the equation while the (hl) is from the previous iteration.

here is my code, I'm using a (for loop), but the problem is that it produces the same value of the intitial (hl) for all 298 outputs. Any ideas what is wrong?

Al=36000;

Qr=31.5;

Ai=3.14*(150/2)^1/2;

Time=table2array(wl(:,1));

wl_sea=table2array(wl(:,3));

wl_lagoon=table2array(wl(:,4));

ho=20.62949/100;

deltat=0;

hl=23.908655/100;

kf=0.3;

% the first step is to use the first known lagoon water level to calculate

% the next level using the sea water level as input

hl0=hl+(deltat*(Ai/Al))*((2*9.81)^0.5/kf)*((ho-hl)/(abs(ho-hl)^0.5)+(deltat*(Qr/Al)))

ho=wl_sea;

for i=1:1:298

hi = hl0;

h(i)=hi;

hi = hi+(deltat*(Ai/Al))*((2*9.81)^0.5/kf)*((ho-hi)/(abs(ho-hi)^0.5)+(deltat*(Qr/Al)))

end

[Star Strider]

The ‘hl0’ variable is a scalar that never changes (created outside the loop). In each iteration of the loop, you overwrite ‘hi’ with that same value, then store it as ‘h’. So nothing ever changes.

You need to solve that, since I have no idea what you want to do.

[Tarek Zaqout]

well that's the thing I'm trying to do. I want to calculate an initial value of hl0. Then I want to use it one time for the next calculation. the following calculation should produce the new value and so on.

[Star Strider]

Another problem that I just now noticed is that ‘deltat’ is 0, so that makes the entire rest of the expression (to the right of it) equal to 0. If you make ‘deltat’ something other than 0, ‘h’ changes.

[Tarek Zaqout]

I change deltat before running the loop. deltat=0 this is also for the first iteration.

[Tarek Zaqout]

alright to make it simpler.

hi=0.2391;

then assuming all variables are defined.

for i=1:298

hi = hi+(deltat*(Ai/Al))*((2*9.81)^0.5/kf)*((ho-hi)/(abs(ho-hi)^0.5)+(deltat*(Qr/Al)))

end

[Peter Perkins]

Loop issues aside, you definitely can make this (and the other two lines like it)

Time = table2array(wl(:,1))

simpler:

Time = wl.Time % or whatever the var name is