Scientific computing loops and iterations

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Hello
I am trying to simulate a process with the help of an m.file. The process is containing multiple structures created previously, although i think the looping sequence I am using has a fault in the way i structure it.
The process is as follows
Initially there is the main if loop which if satisfied it will enclose the consequential simulations:
if Demand <= Ewave; % this is the main limitation to be satisfied
count = length(Ewave) % Based on the length of the input file to create a counter for the loops
for count = (1:count-1)
if E_comp>P_comp
m_air_flow = (P_comp_joule *E_comp_joule*n_isc*n_mech)/(Cp_air*T_amb*((Press_r^inverse)-1));
T_out_comp = T_amb*(1+(1/n_isc)*((Press_r^inverse)-1));
elseif E_comp<=P_comp
m_air_flow = (P_comp_joule*E_comp_joule *n_isc*n_mech)/(Cp_air*T_amb*(Press_r^inverse));
T_out_comp = T_amb*(1+(1/n_isc)*(Press_r^inverse));
end
end
E_to_store = E_comp*Default.n_comp;
E_to_store_joule = E_to_store * 1000000;
count = length(E_to_store_joule)
for count = (1:count-1)
% This is the main portion of interests, the initial values are to calculated once for the 1st iteration
M_cavern(count) = E_to_store_joule(count) / (Cp_air*T_amb*(Press_r^inverse)-1);
P_cavern(count) = Default.P_cavern;
T_cavern(count) = Default.T_cavern;
% Then the 1st iteration results are used, and from that point on the counter has to ensure that the next iteration will use the previous quantity to calculate the new quantity
M_cavern(count+1) = M_cavern(count)+(m_air_flow-m_air_flow*Default.dm);
P_cavern(count+1) = P_cavern(count) - (Default.dP*Press_r);
T_cavern(count+1) = T_cavern(count) - (Default.dt*T_cavern(count));
end
Essmin = Load.N_ex *ho;
Vssmin_MWh =Essmin/DOD;
Vssmin_joule = Vssmin_MWh*3600000;
mass_flow_guar = (Vssmin_joule *P_cavern*DOD)/(ho*T_cavern*R_g);
if count==1
Tt3(count) = T_cavern+(T_cavern.*n_pre);
Tt4(count) = (Cp_air/Cp_gas)*(lamda*Ma/((lamda*Ma)+1))*...
Tt3a+(Hu/(((lamda*Ma)+1)*Cp_gas));
if Tt4(count)=<Ttmax;
Tt5(count) = Tt4(count)*(1-n_isT*(1-(1/(expansion_ratio^inverse))));
end
end
end
As you can see, my focus is to create a loop sequence which i can expand later on in various loops, the initial quantities are calculated (1st) then until the end of the (Nth) iteration the process should be 1st,2nd=(2nd-1*,,) .... Nth=(Nth-1* ...)
Can anyone help me, in suggesting or if i has faulty set-up the looping sequence.
thank you in advance

Accepted Answer

Geoff Hayes
Geoff Hayes on 19 Sep 2014
George - I did notice a couple of pieces of your code which I'll just highlight here. In your for loops you do the following
count = length(Ewave) % or something similar
for count = (1:count-1)
While the above works, it does seem a little confusing to name your index variable to that of one that you are indexing/iterating over. Consider instead
for u=1:count-1
or something similar.
In your first for loop, you do the following
for count = (1:count-1)
if E_comp>P_comp
m_air_flow = (P_comp_joule *E_comp_joule*n_isc*n_mech)/(Cp_air*T_amb*...
((Press_r^inverse)-1));
T_out_comp = T_amb*(1+(1/n_isc)*((Press_r^inverse)-1));
elseif E_comp<=P_comp
m_air_flow = (P_comp_joule*E_comp_joule *n_isc*n_mech)/(Cp_air*T_amb*...
(Press_r^inverse));
T_out_comp = T_amb*(1+(1/n_isc)*(Press_r^inverse));
end
end
Note how none of the iterations of the loop depends upon count, and so you are calculating the same values for m_air_flow and T_out_comp at each iteration. Is this loop necessary, or should you be making use of some other variable (array) in these equations that would depend upon count?
Note also how T_out_comp is not used in your block of code (at least not in the portion that you have included in your question). Should it be used somewhere?
In your second for loop
for count = (1:count-1)
% This is the main portion of interests, the initial values are to calculated
% once for the 1st iteration
M_cavern(count) = E_to_store_joule(count) / (Cp_air*T_amb*(Press_r^inverse)-1);
P_cavern(count) = Default.P_cavern;
T_cavern(count) = Default.T_cavern;
% Then the 1st iteration results are used, and from that point on the counter
% has to ensure that the next iteration will use the previous quantity to
% calculate the new quantity
M_cavern(count+1) = M_cavern(count)+(m_air_flow-m_air_flow*Default.dm);
P_cavern(count+1) = P_cavern(count) - (Default.dP*Press_r);
T_cavern(count+1) = T_cavern(count) - (Default.dt*T_cavern(count));
end
On each iteration, you update the count and count+1 elements of the M_cavern, P_cavern and T_cavern arrays. On the subsequent iteration, you update the count+1 and count+2 elements of these same arrays and so overwrite the second block of calculations from the previous iteration i.e. {1,2} get updated when count==1, {2,3} get updated when count==2, {3,4} get updated when count==3, etc. Is this intentional, or do you want to skip by two at each iteration
for u=1:2:count-1
With the above change to the indexing in this loop, you would update {1,2} when u==1, {3,4} when u==3, etc.
Note that the arrays M_cavern, P_cavern and T_cavern are not used outside of this for loop.
The last if block is
if count==1
Tt3(count) = T_cavern+(T_cavern.*n_pre);
Tt4(count) = (Cp_air/Cp_gas)*(lamda*Ma/((lamda*Ma)+1))*...
Tt3a+(Hu/(((lamda*Ma)+1)*Cp_gas));
if Tt4(count)=<Ttmax;
Tt5(count) = Tt4(count)*(1-n_isT*(1-(1/(expansion_ratio^inverse))));
end
end
What does count refer to - the length of which array? What are Tt3,*Tt4*, and Tt5?
  5 Comments
Geoff Hayes
Geoff Hayes on 22 Sep 2014
Since the first for loop doesn't depend on count, just remove it and use simply
if E_comp>P_comp
m_air_flow = (P_comp_joule *E_comp_joule*n_isc*n_mech)/...
(Cp_air*T_amb*((Press_r^inverse)-1));
T_out_comp = T_amb*(1+(1/n_isc)*((Press_r^inverse)-1))
else
m_air_flow = (P_comp_joule*E_comp_joule *n_isc*n_mech)/...
(Cp_air*T_amb*(Press_r^inverse));
T_out_comp = T_amb*(1+(1/n_isc)*(Press_r^inverse))
end
As for the overwriting of the data on subsequent iterations, just change the step size from the default of 1 to 2. Replace (in the second for loop)
for count = (1:count-1)
with
for k=1:2:(count-1)
That way, you will update array indices 1 and 2 when k==1, 3 and 4 when k==3, etc. because now our step size is 2. Try stepping through the code (in the debugger) and observe these changes. (Note that I've switched the index from count to k.)
George
George on 24 Sep 2014
Thank you very much for your patience and help, form your first comments i changed the count=1:(count-1) with u , so as not to contradict.
I will try it to run in section by section, hopefully it will run and i think i have understood how you do a loop in reverse order, I will post the proper code when it run so other may have visual help.

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