Help debugging a code? Says function makes an error but when I run it, it returns the correct output...

I'm having trouble with the following assignment:

Write a function called sort3 that takes a 3-element vector as its sole arguments. It uses if-statements, possibly nested, to return the three elements of the vector as three scalar output arguments in non- decreasing order, i.e., the first output argument equals the smallest element of the input vector and the last output argument equals the largest element. NOTE: Your function may not use any built-in functions, e.g., sort, min, max, median, etc.

Here is what I've done so far:

function [a,b,c]=sort3(A)
a= A(1); b=A(2); c=A(3);
if (a<=b)&& (b<=c)
    if a<b && b<c
        output= [a b c]
    elseif(a==b)&& b<c
        output= [a b c]
    elseif a<b && (b==c)
        output= [a b c]
    else a==b==c
        output= [a b c]
    end
elseif (a<= c)&& (c<=b)
    if (a<c)&& (c<b)
        output= [a c b]
    elseif (a==c)&& a<b
        output= [a c b]
    elseif a<c && (c==b)
        output= [a c b]
    else a==c==b
        output= [a c b]
    output = [a c b]
    end
elseif (b<=c) && (c<=a)
    if b<c && c<a
         output= [b c a]
    elseif (b==c)&& c<a
         output= [b c a]
    elseif b<c &&(c==a)
         output= [b c a]
    else b==c==a
         output= [b c a]
    end 
elseif (b<=a) && (a<=c)
    if b<a && a<c
         output= [b a c]
    elseif (b==a)&& b<c
         output= [b a c]
    elseif b<c &&(c==a)
         output= [b a c]
    else b==c==a
         output= [b a c]
    end 
elseif (c<=a) && (a<=b) 
   if c<a && a<b
         output= [c a b]
    elseif (c==a)&& a<b
         output= [c a b]
    elseif c<a && (a==b)
         output= [c a b]
    else c==a==b
         output= [b c a]
    end 
else (c<=b) && (b<=a)
    if c<b && b<a
         output= [c b a]
    elseif (c==b)&& b<a
         output= [c b a]
    elseif c<b && (b==a)
         output= [c b a]
    else b==c==a
         output= [b c a]
    end 
end

I ran it through an autograder and it said:

    Feedback: Your function performed correctly for argument(s) [1 2 3]
    Feedback: Your function made an error for argument(s) [1 3 2]

But when I set A= [1 3 2], it seems to return the output [1 2 3].

Also -- I totally realize that my code is very inefficient. What are some ways I could make my code more efficient?

Thank you!

Answer 1

[per isakson]

IMO: Your code is a nightmare to debug and I will not try.

There is a problem with output. It's not used as output.

Proposal: See varargout, Variable-length output argument list and replace

function [a,b,c]=sort3(A)

by

function  varargout = sort3(A)

and all the

output = [ ...]

by

varargout = { ... }; % e.g.
varargout = { b, c, a };

If that doesn't help see Bubble sort

In response to comment:

Add this line at the end of your code

a = out(1); b = out(2); c = out(3);

Replace

else b==c==a

by

elseif  b==c && c==a

or whatever it's intended to be

[Hye Sun Choi]

I think the purpose of this assignment is not to use any built-in functions unfortunately...

[per isakson]

What do you regard as a built-in function? varargout ???

I added an alternative solution to my answer.

[Walter Roberson]

https://www.mathworks.com/matlabcentral/answers/38787-what-can-be-programmed-without-any-built-in-functions