MATLAB: Can someone explain me how to make this loop efficiently

arrayforfor loopif statementMATLABvectors

Hello Mathworks community!
I'm having a bit of trouble trying to code a for loop. This is my code so far.
randomNumber1 = 100;
randomNumber2 = 150;
out(1)= 0;
B = 4;
for idx = 2:1:numel(A)
    if idx <=(B)
        ArrayValue = SomeArray(1);
        if % first condition

            out(idx) = ((out(idx - 1)) - randomNumber1);
        elseif % second condition

            out(idx) = ((out(idx - 1)) - randomNumber2);
        elseif % third condition

            out(idx) = (out(idx - 1) + ArrayValue);
        end
    elseif idx >(B) && idx <= (2*B)
         ArrayValue = SomeArray(2);
         if % first condition
             out(idx) = ((out(idx - 1)) - randomNumber1);
         elseif % second condition
             out(idx) = ((out(idx - 1)) - randomNumber2);
         elseif % third condition
             out(idx) = (out(idx - 1) + ArrayValue);
         end
    elseif idx >(2*B) && idx <= (3*B)
          ArrayValue = SomeArray(3);
          % It keeps going until I've used every "SomeArray" value
     end
end
As you can see, I have to repeat all the statements as many times as values I have inside my vector: SomeArray
The code works as it should, but I'm well awared that this is not how you do it properlly. I know aswell that it is possible to only state the conditions one time, I'm just not sure how to do it.
Could someone help me out?
Thank's!
Santos

Best Answer

I think the key is coming up with an expression that gives you the index for someArray from the current loop index. Something like this:
randomNumber1 = 100;
randomNumber2 = 150;
out(1)= 0;
B = 4;
for idx = 2:1:numel(A)
    k = ceil(idx/4); % index into someArray
    ArrayValue = SomeArray(k);
    if % first condition
        out(idx) = ((out(idx - 1)) - randomNumber1);
    elseif % second condition
        out(idx) = ((out(idx - 1)) - randomNumber2);
    elseif % third condition
        out(idx) = (out(idx - 1) + ArrayValue);
    end
end
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