seeking help with a for loop syntax

Hi there,

I'm trying to write a simple for loop to simulate how the state of charge of an electric vehicle battery decreases as journeys are made. I specify the following variables before the for loop:

1. The number of journeys
2. The initial state of charge of the battery
3. The departure time and arrival time of each journey

I want to decrease the initial state of charge with each iteration of the for loop. The calculation is just the (arrival time - departure time)*1.5. I'm just learning matlab and I have attempted it below but it is completely wrong. I'd appreciate any help.

JN = 3; % Number of journeys
dt1=2; % departure time 1
at1=5; % arrival home time 1 
dt2=8; % departure time 2
at2=11; % arrival time 2
dt3=8; % departure time 3
at3=11; % arrival time day 2
SOC0 = 100; % Initial state of charge  

for i=1:JN

     SOC(i) = SOC (i-1) - (at(i)-dt(i))*1.5

end

[dpb]

for i=1:JN
   SOC(i) = SOC (i-1) - (at(i)-dt(i))*1.5

What's the index for i=1 for the term SOC(i-1)? Matlab arrays are 1-based.

Also, the space there undoubtedly is a syntax error. You need as starters

at=[5 11 11]; % arrival home times 
dt=[2  8  8]; % departure times
SOC(1)=SOC0;
for i=1:JN
  SOC(i) = SOC(i-1) - (at(i)-dt(i))*1.5
end

ERRATUM:

After that I still didn't fix the 0-array addressing...changed my course in midstream and then didn't finish...

for i=1:JN
  SOC(i+1) = SOC(i) - (at(i)-dt(i))*1.5;
end

This will give you a result for JN+1 entries with the first being the initial and the 2nd on the result after the previous leg.

In general you'll want to learn to preallocate as well -- that is, set

SOC=zeros(JN+1,1); 
SOC(1)=SOC0;

before the loop.

Then, the "Matlab way" would be to vectorize the computation and eliminate the loop...

>> SOC0=100;
>> SOC=[SOC0 cumsum(SOC0-at.*dt*1.5)]
SOC =
 100    85    53    21
>>

[John]

Thank you for your help

Answer 1

[dpb]

For the loop solution you've got to fix the references to start at one. One way is sotoo--

SOC0=100;
at=[5 11 11]; % arrival home times 
dt=[2  8  8]; % departure times
SOC=zeros(JN+1,1); 
SOC(1)=SOC0;
for i=1:JN
SOC(i+1) = SOC(i) - (at(i)-dt(i))*1.5;
end

Then, the "Matlab way" would be to vectorize the computation and eliminate the loop...

>> at=[5 11 11]; dt=[2  8  8];
>> SOC0=100;
>> SOC=[SOC0 cumsum(SOC0-at.*dt*1.5)]
SOC =
100    85    53    21
>>