Plotting values from a set of nested if-else statements in while loop nested in a for loop

The code below produces a plot 1000 by 1000 and my goal is to plot each value of length after it iterates through the while loop. what ends up happening here is my function only returns the last value of length.

the purpose of the function is to retrieve to length of each sequence: s(n) = s(n-1)/2 if s(n-1) > 1 and even

s(n) = 3*s(n-1) + 1 if s(n-1) > 1 and odd

If i remove the comments i can loop through 1000 times and have the value of length printed each time, but i need to store that value in order to plot it(i think).

Any help would be appreciated

%%%%%%%%%%%%%%%%%%%%%%

v = 1:1000;

plot(v,xyz(v),'r+-');

%axes' bounds and labels

axis([0 1000 0 1000]);

xlabel('s(x)');

ylabel('Length of s(x)');

%Title

title('XYZ Sequence');

function [length] = xyz(v)

your_int = 1;

count = 1;

for x_= v

length = 1;

your_int = your_int * count;

while( your_int ~= 1) %length of sequence is retrieved when your_int = 1

%fprintf("\nYour integer = %10d", your_int);

%un_comment the line above to see each number in the sequence

if( mod(your_int, 2) == 0)

your_int = your_int / 2; %s(n) = s(n-1)/2 if s(n-1) > 1 and even

else

your_int = 3*your_int + 1; %s(n) = 3s(n-1) + 1 if s(n-1) > 1 and odd

end

length = length + 1; %length of the sequence

end

count = count + 1; %multiply by your_int to increment

%fprintf("\n\tThe length of s(%4d) is %4d", (count-1), length);

%un_comment the line above to see the value of length after each for loop iteration

end

end

Answer 1

[Jyotsna Talluri]

Consider an array inside the function and append the length each time to that array in a for loop ..k is the array considered

function k = xyz(v)
        your_int = 1;
        count = 1;
        k=[];
        for x_= v
        length = 1;
        your_int = your_int * count;  
            while( your_int ~= 1)          
            	if( mod(your_int, 2) == 0)
        		your_int = your_int / 2;      
                else
        		your_int = 3*your_int + 1;  
                end
                length = length + 1;      
            end  
             k=[k length];
             count = count + 1;            
        end
        end

[Nathan Preslar]

Thank you so much! I knew it was some small change like that. I had beed putting that array inside the function within the loops, so I kept getting 112 - the last number. Thank you so much.

[Stephen23]

"...and append the length each time to that array in a for loop"

The MATLAB documentation recommends preallocating arrays before the loop:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

Note also that the code shadows the inbuilt length function.

Note that the code alignment is very inconsistent: irregular code alignment is one way that beginners hide basic bugs in their code. You should use the default alignment of the MATLAB Editor: select all code text, press ctrl+i.

Answer 2

[Stephen23]

An improved version of your script, without the poor practices shown in Jyotsna Talluri's answer:

V = 1:1000;
N = numel(V);
L = ones(1,N); % preallocate output array.
for k = 1:N
    s = V(k);
    while s>1
        if mod(s,2) % odd
            s = 3*s + 1;
        else % even
            s = s/2;
        end
        L(k) = L(k)+1;
    end
end

Giving:

>> L(1:10)
ans =
    1    2    8    3    6    9   17    4   20    7