Fix an undefined variable in a nested if function?

So here's a part of my code:

if ((destination_one > 0)&&(location_caller > 0))||((destination_one < 0)&&(location_caller < 0))
                dc1 = abs(destination_one - location_caller);
            elseif ((destination_one > 0)&&(location_caller < 0))||((destination_one < 0)&&(location_caller > 0))
                dc1 = (abs(destination_one) + abs(location_caller));
            end

              if ((destination_two > 0)&&(location_caller > 0))||((destination_two < 0)&&(location_caller < 0))
                  dc2 = abs(destination_two - location_caller);
              elseif ((destination_two > 0)&&(location_caller < 0))||((destination_two < 0)&&(location_caller > 0))
                  dc2 = (abs(destination_two) + abs(location_caller));
              end

              condition_4 = [(dc2 > dc1), (dc2 < dc1)];
              check_condition_4 = sum(condition_4);

Whenever I try to run it against certain test cases, it will return an error saying that, for condition_4, dc2 is undefined. Is my end statement placement wrong? Thanks in advance.

Answer 1

[Walter Roberson]

In the first group, neither branch is true if either value is 0 exactly. There are probably also failures if one of the values is NaN.

If you have an if/elseif that defines variables then you should always prepare for the possibility that neither branch is true and make sure the variable is defined anyhow.

If you are sure that the elseif is testing the exact opposite of the if, then why bother to elseif? Why not just if/else ?

Your first test is equivalent to

(destination_one ~= 0) && (location_one ~=0) && sign(destination_one) == sign(location_one)

and the elseif is equivalent to

(destination_one ~= 0) && (location_one ~=0) && sign(destination_one) ~= sign(location_one)

(except perhaps in what happens if a value is NaN)