Is there any alternative to if statements inside for loops?

5 次查看（过去 30 天）
Theo
Theo 2012-5-17
Hello, my code has many parts like this :
for i=1:8760
for j=1:Ni
if Ns*Vm(i) < Vi_min
Pin(i,j) = 0;
else
if year==1
r_y=0;
else
r_y=r_pv;
end
eta_m=eta_mppt(Ns*Np*Pm(i));
Pin(i,j) = (1 - As_I(i,j)*SIF/Ns*Np*Lpv1*Lpv2)*(1-n_l_dc*PL_dc)*Ns*Np*eta_m*(1 - r_y*year)*Pm(i);
end
end
end
It takes a long time to execute due to the if statement inside for loops. I would like to ask if there is an alternate implementation to that. Thanks

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采纳的回答

Walter Roberson
Walter Roberson 2012-5-17
1) logical indexing
2) Ns, Vm(i), vi_min are all invariant in your "j" loop, so there is no point doing the "j" loop in that condition. Likewise, eta_m is independent of j.
if Ns*vm(i) < Vi_min
Pin(i,1:ni) = 0;
else
eta_m=eta_mppt(Ns*Np*Pm(i));
for j = 1 : Ni
....
end
end

更多回答（3 个）

Dr. Seis
Dr. Seis 2012-5-17
Do you pre-allocated "Pin", if not... then before the for-loops put:
Pin = zeros(8760,Ni);
The inside of your for-loops will become:
if Ns*Vm(i) >= Vi_min
if year==1
r_y=0;
else
r_y=r_pv;
end
eta_m=eta_mppt(Ns*Np*Pm(i));
Pin(i,j) = (1 - As_I(i,j)*SIF/Ns*Np*Lpv1*Lpv2)*...
(1-n_l_dc*PL_dc)*Ns*Np*eta_m*(1 - r_y*year)*Pm(i);
end
That should help run-time a bit.
Jan
Jan 2012-5-17
The if -condition does not depend on the counter of the inner loop:
for j=1:Ni
if Ns*Vm(i) < Vi_min
Then you can move it outside:
if Ns*Vm(i) >= Vi_min
for j=1:Ni
The pre-allocation mentioned by Elige will be more important.
Theo
Theo 2012-5-17
Thanks a lot!! , there has been a great improvement. Last question , is there anything else that can be done about those 4 for loops? I appreciate your help.
for i=1:8760
for j=1:Ni
if Pin(i,j)>Pi_sc
if Pin(i,j)<=Pi_na(i)
eta=eta_inv(Pin(i,j));
Po(i,j) = eta*Pin(i,j);
else
eta=eta_inv(Pi_na(i));
Po(i,j) = eta*Pi_na(i);
end
else Po(i,j) = 0;
end
end
end
for i=1:8760
if P_plant(i)>P_plant_max
P_plant(i) = P_plant_max;
end
end
for i=1:8760
if P_plant(i) > P_grid_max(i)*(1 + (year-1)*Sg)
P_plant(i) = P_grid_max(i)*(1 + (year-1)*Sg);
end
end
for i=1:8760
for j=1:Ni
if Pin(i,j) < 0
Pin(i,j) = 0;
end
end
end
  1 个评论
Walter Roberson
Walter Roberson 2012-5-17
Well, for example, you can replace
for i=1:8760
if P_plant(i)>P_plant_max
P_plant(i) = P_plant_max;
end
end
with
P_plant = min(P_plant, P_plant_max);
with no loop.
Likewise, consider
Pin = max(Pin,0);

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