Is there any alternative to if statements inside for loops?

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

[James Tursa]

Please use formatting for your question so we can read the code.

Answer 1

[Walter Roberson]

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

[Jan]

Walter, you have been faster. +1

Answer 2

[Dr. Seis]

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.

Answer 3

[Jan]

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.

Answer 4

[Theo]

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

[Walter Roberson]

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);