Battery charge simulation not clipping properly as it iterates

Question

My code for simulating a batterylevel-state throughout a year in 15min-steps doesn't work.

There is a certain list-inputs which simulates the charge state and the batterylevel-state, additionally maximum capacity and minimum capacity(because of discharge-depth) and L as start charging state

maxk=10;
mink=2;
L=5;
chargelevel= {-0.1,-0.1,-0.2, ...(more than 35000 other positive/negative values)...,-0.2,-0.1};
batterylevel=Table[L, {n, 0, 35040}]

which is used by

For[i = 1, i < 35040, i++,
  Which[mink <= (batterylevel[[i - 1]] + chargelevel[[i]]) <= maxk,
    batterylevel[[i]] = (batterylevel[[i - 1]] + chargelevel[[i]]), 
    batterylevel[[i]] <= mink, batterylevel[[i - 1]] = mink, 
    batterylevel[[i]] >= maxk, batterylevel[[i - 1]] = maxk
    ];];
ListPlot[batterylevel]

batterylevel`

The function should be working like this: The loop defines that i is running over the whole thing 35040 times and the batterylevel from step i-1 should be summed up with the chargelevel from step i. If the charge state reaches or falls below 2kWh, it should stay at mink=2kWh and don't add negative chargelevel-rates anymore and go on with looping until there is a positive chargelevel, then it should add chargerates again and load the battery until maxk=10kWh and then stop again at 10kWh and go on with looping. When it reaches negative states, it should discharge again until 2 and so on.

So far i successfully modeled this thing in excel and it worked flawlessly. The crazy thing is that it worked yesterday after trying it a few times and it matched with the result in excel.

Today since i loaded the same notebook (!) it doesn't give me the same output anymore because according to the batterylevel-output it discharges till or below 2 (since it's more likely to reach mink=2 first) and then it starts at L=5 again, adding or substracting the rates according to the chargelevel. The same happens when reaching maxk=10, it just jumps back to L=5. It doesn't jump with the chargelevel-list though.

According to PlotList it looks like this, where you can clearly see that it jumps back:

I even tried to rewrite the loop with while and the conditional with If and Switch, where i get the same result (although If is made like the one in Excel).

Can somebody help me out with this please?

Answer 1

Your code shows you are somewhat confused about the indices. Here is some code that is more Mathematica idiomatic and which makes keeping the indices straight much easier. I am running the simulation with a 24 hour step to cut down the data plotted. Should work just a well with your time step.

maxk = 10;
mink = 2;
steps = 365;
batterylevel = ConstantArray[0, steps];
batterylevel[[1]] = 5;

SeedRandom[7]; chargelevel = RandomReal[{-.75, .75}, steps];

Do[Module[{next},
   next = batterylevel[[i - 1]] + chargelevel[[i]];
   Which[
    mink < next < maxk, batterylevel[[i]] = next,
    next <= mink, batterylevel[[i]] = mink,
    next >= maxk, batterylevel[[i]] = maxk]],
  {i, 2, steps}];

ListPlot[batterylevel]

You can see the clipping at 2 and 10 is now handled correctly.

Update 1

Using the built-in Mathematica function Clip, your simulation can be reduced to

Do[
  batterylevel[[i]] = Clip[batterylevel[[i - 1]] + chargelevel[[i]], {mink, maxk}],
  {i, 2, steps}]

Update 2

As you become more experienced with Mathematica, you will come to appreciate that your simulation can be expressed even more concisely. In Mathematica there is no need to create a batterylevel array.

SeedRandom[7];
 With[{maxk = 10, mink = 2, initk = 5, steps = 365},
   Module[{chargelevel},
    chargelevel = RandomReal[{-.75, .75}, steps];
    ListPlot[FoldList[Clip[#1 + #2, {mink, maxk}] &, initk, chargelevel]]]]

The plot produced by this code is exactly the same as the one shown above.