Index exceeds the number of array elements (6)

Hi guys, I know there're some similar questions around the comunity but I didn't find an answer to understand my problem.

I'm writing a code to sort an vector without using "sort" function, however matlab returns me an error that tells :"Index exceeds the number of array elements (6); min = q(s);". I put "min" equal to the element of vector "q" with index "s" so I don't understand why matlab tells me this error.

I hope you can help me, thanks.

q = [3 1 -1 4 2 0 ] 
qRiserva = 0;  % variable to temporarily keep the element of q(s)
s = 1;         % index for outer 'for cycle'
min = q(s);
max = q(1);
i = 1;         % index for deeper 'for cycle'


for s = s :length(q)
    
        for i = s: length(q)
                    if q(i) <= min
                                     qRiserva(s) = q(s)
                                     min = q(i)
                                     q(s) = min
                                     q(i) = qRiserva(s)
                   end
        end

        s = s+1;
        min = q(s); 
       
end  

[Star Strider]

Please do not use ‘min’ and ‘max’ as variable names. They are built-in MATLAB functions, and using them as variables will cause you no end of problems.

[Alessandro Marutti]

Thank you for your advice but also changing the name of the variable it gives me the same error.

I think matlab thinks I want turn "min" variable in a vector that is a copy of each element of q

[Star Strider]

Do not increment ‘s’ in the loop:

s = s+1;

Leave that to the for function. (Changing the index variable in a for loop does not actually change the index variable that for uses, anyway. The for function ignores them.) With that change, your code will not throw the error you reported.

It is necessary to change your ‘min’ and ‘max’ variable names so that they do not overshadow the MATLAB functions, even though you do not use them in your posted code.

[Adam]

You shouldn't have statements like

s = s+1;

in a for loop for which s is the loop control. s is changed each iteration according to

for s = s :length(q)

Either use s as it is or use a different variable if you really want s + 1 (or just code s + 1 instead of assigning it back to s).

I can't remember off the top of my head what Matlab does with statements that change the loop variable, but if it is executed as stated then the final time round the loop s will be equal to the length of q (i.e. the last valid index). Then you add 1 to it and try to use that to index into q, which clearly will not be valid.

[Alessandro Marutti]

OK thanks guys, now it doesn't show me the error but the code doesn't work either.

If I write the code as a 6-times sequence of the deeper "for loop" it works but if I write the code as in the first message (inside another "for") it doesn't work

[Star Strider]

You are apparently writing a °bubble sort’ algorithm. The essence of that is to compare adjacent elements, and then switch their order (depending on whether you are sorting in the ascending or descending mode), keeping track of the number of switches in each iteration. Keep doing that until there are no more switches.

[Alessandro Marutti]

I moved "min = q(2)" (to whom I changed name) from the bottom to the top between the two "for loops" and now everything works right.

Thanks a lot to everybody your're super efficient!