Need to run two counters in a foor loop

Question

Adil Ali 2021-5-1

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https://ww2.mathworks.cn/matlabcentral/answers/818870-need-to-run-two-counters-in-a-foor-loop

回答： Steven Lord 2021-5-1

Here is my problem.

I have two lists of the same length = A. The lists are P and T.

I anticipate to be running a for loop (for ls=1:A) embedded in another foor loop (for i = 1:ls).

Below is what I would like to get when the loops are running:

ls = 1

i = 1

P(1) + T(1);

ls = 2

i = 1

P(1) + T(2);

i = 2

P(2) + T(1);

ls = 3

i = 1

P(1) + T(3);

i = 2

P(2) + T(2);

i = 3

P(3) + T(1);

ls = 4

i = 1

P(1) + T(4);

i = 2

P(2) + T(3);

i = 3

P(3) + T(2);

i = 4

P(4) + T(1);

....... and so on until the lenght of A

I need help in making the counter with T go backwards from the value of ls. Create a dynamic vector in the loop is not a good idea

for ls=1:A

K = ls:-1:1

for i=1:ls

P(i)+T(K(i))

end

Id appreciate for someone's help as I have spent 3 hours trying to come up with a solution for this and got to no where. Maybe a formula instead of the "????" below.

for ls=1:A

for i=1:ls

P(i)+T(????)

end

Thank you.

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Answer 1

dpb 2021-5-1

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编辑：dpb 2021-5-1

If you describe the real problem to be solved instead, it'll lead to more efficient getting to the right answer, but if the result is to simply sum the two variables in obverse order, you don't need loop at all --

S=P+flipud(T);

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Adil Ali 2021-5-1

That is right. My apologies. Here is the acutal problem.

I am simulating emittion of laser pulses. I create pre allocated array of zeros

pulses=zeros(length(t),4); %% need other columns for other information but the first column needs to be distance travelled by each pulse at time = t.

Then i run my laser for time = LaserOnTime and the pulses are emitted (one after the other) at PRF = 500kHz. so I create an array

t = 1:1/PRF:LaserOnTime;

for ls=1:length(t)

k = ls:-1:1;

for i=1:(ls)

if(pulses(i,1)<=2*Altitude)%%increment the distance of pulse until 2*alt is %achieved

pulses(i,1) = pulses(i,1) + SpeedOfLight*t(k(i)); %%increment the %distance of each pulse

end

This works but k=ls:-1:1 changes its size at each counter and this is not the most idea solution.

Thank you.

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Answer 2

David Fletcher 2021-5-1

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One way of recreating your original sequence via the loops would be:

A=ones(1,5);
for iterator=1:length(A)
    sub=0;
    fprintf('outer loop: %d\n',iterator)
    for ls=1:iterator
        fprintf('P(%d) + T(%d)\n',ls,iterator-sub)
        sub=sub+1;   
    end
    iterator=iterator+1;
end

This gives:

outer loop: 1

P(1) + T(1)

outer loop: 2

P(1) + T(2)

P(2) + T(1)

outer loop: 3

P(1) + T(3)

P(2) + T(2)

P(3) + T(1)

outer loop: 4

P(1) + T(4)

P(2) + T(3)

P(3) + T(2)

P(4) + T(1)

outer loop: 5

P(1) + T(5)

P(2) + T(4)

P(3) + T(3)

P(4) + T(2)

P(5) + T(1)

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Answer 3

Steven Lord 2021-5-1

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F = 3;
S = 4;
for first = 1:F
    fprintf("Counting up, first is %d\n", first)
    for second = S:-1:1
        fprintf("Counting down, second is %d\n", second)
        fprintf("The equivalent counting up inner counter would be %d\n", S-second+1)
    end
    fprintf(" \n")
end
Counting up, first is 1
Counting down, second is 4
The equivalent counting up inner counter would be 1
Counting down, second is 3
The equivalent counting up inner counter would be 2
Counting down, second is 2
The equivalent counting up inner counter would be 3
Counting down, second is 1
The equivalent counting up inner counter would be 4
 
Counting up, first is 2
Counting down, second is 4
The equivalent counting up inner counter would be 1
Counting down, second is 3
The equivalent counting up inner counter would be 2
Counting down, second is 2
The equivalent counting up inner counter would be 3
Counting down, second is 1
The equivalent counting up inner counter would be 4
 
Counting up, first is 3
Counting down, second is 4
The equivalent counting up inner counter would be 1
Counting down, second is 3
The equivalent counting up inner counter would be 2
Counting down, second is 2
The equivalent counting up inner counter would be 3
Counting down, second is 1
The equivalent counting up inner counter would be 4
 