if statement didn't executed in a loop

Hi all, I have problem on the if statement that inside can't be executed which makes other operations in the code cannot be run. My code is as follow, the problems is occurred at the "if isequal(time(i),off_tt)" parts where the variables 'k' didn't increment.

    k = 0; on_t = 2;off_t = 2;
    for i=1:length(time)
        on_tt = (on_t*(k+1))+(off_t*k)
        off_tt = (on_t*(k+1))+(off_t*(k+1))

        if(time(i) ~= off_tt)
            if (on_t == 0)
                ref_speed_left = [ref_speed_left, 0];
                ref_speed_right = [ref_speed_right, 0];
            elseif (off_t == 0)
                ref_speed_left = [ref_speed_left, ref_speedR];
                ref_speed_right = [ref_speed_right, ref_speedL];
            elseif (time(i) < on_tt)     %ans == 0
                ref_speed_left = [ref_speed_left, ref_speedR];
                ref_speed_right = [ref_speed_right, ref_speedL];
            elseif (time(i)>= on_tt && time(i) < off_tt+1)
                if isequal(time(i),off_tt)       %problems at this if statement
                        k=k+1;                   %k didn't increment when it 
                end                              %met the requirement

                ref_speed_left = [ref_speed_left, 0]
                ref_speed_right = [ref_speed_right, 0]
            end
        end    
    end

May I know any solutions for this, your helps is much appreciate. Thanks you.

[Azzi Abdelmalek]

Can you post values of ref_speedR and others variables, to allow testing your code

[Shawn Chang]

time = 0.05:0.05:14.95;

ref_speedR = 0.3595;

ref_speedL = 0.3693;

Answer 1

[Ilham Hardy]

 for i=1:length(time)

        k=i %correction

        on_tt = (on_t*(k+1))+(off_t*k)
        off_tt = (on_t*(k+1))+(off_t*(k+1))

You declare k=0, therefore k is 0.

[Shawn Chang]

"k=0" is used to initialize the k.

When on_tt and off_tt value has been met and k will be increment by 1 to obtain a new on_tt and off_tt.

eg. last value in time(i) = 15, on_t = 2, off_t = 2;

When k = 0; on_tt = 2, off_tt = 4;

When k = 1; on_tt = 6, off_tt = 8;

until either on_tt or off_tt reached 15, it will break the for loop.

So, "k=i" cannot be used in this case

Answer 2

[Azzi Abdelmalek]

Are you sur the condition if isequal(time(i),off_tt) is true? I tested your code, the condition is true only for i=80

[Shawn Chang]

I am not sure because logically "if isequal(time(i),off_tt)" is executed when time(i) is equal to off_tt and thus increment the variable, k but it didn't in this case.

eg. when time(80) = 4 and off_tt = 4, but it didn't executed the if statement so I am wonder what mistake I had done in my code.

[Azzi Abdelmalek]

Ok, when time(80) = 4, off_tt = 4, you forget that your code is executed when the condition if(time(i) ~= off_tt) is true, which it is not in this case.

[Shawn Chang]

Ok, but when I changed the code as follow, the code still not working.

k=0;on_t = 2;off_t = 2;
    for i=1:length(time)
        on_tt = (on_t*(k+1))+(off_t*k)
        off_tt = (on_t*(k+1))+(off_t*(k+1))

          if(time(i) ~= off_tt)
              if (on_t == 0)
                  ref_speed_l = [ref_speed_l, 0];
                  ref_speed_r = [ref_speed_r, 0];
              elseif (off_t == 0)
                  ref_speed_l = [ref_speed_l, ref_speedR];
                  ref_speed_r = [ref_speed_r, ref_speedL];
              elseif (time(i) < on_tt)     %ans == 0
                  ref_speed_l = [ref_speed_l, ref_speedR];
                  ref_speed_r = [ref_speed_r, ref_speedL];
              elseif (time(i)>= on_tt && time(i) < off_tt+1)

                  ref_speed_l = [ref_speed_l, 0]
                  ref_speed_r = [ref_speed_r, 0]
              end
          end
          if isequal(time(i),off_tt)
               k=k+1;
          end
      end

[Azzi Abdelmalek]

In this case the condition isequal(time(i),off_tt) occurs one time, look at k, (k=1);

[Shawn Chang]

Yes, k is occurs one time. May I know how to refine the code so that can increment k further?

[Azzi Abdelmalek]

Do you want to increment k each increment of i, if not tell us what is the condition?

[Shawn Chang]

I want to increment k when the element of time(i) is equal to off_tt, so that a new on_tt and off_tt will be obtained and the process run until the for loop is break.

[Azzi Abdelmalek]

you have then to revise your code

Answer 3

[Roger Stafford]

Shawn, look at the third line from the beginning of the for-loop:

 if(time(i) ~= off_tt)

It is an outer condition that must be satisfied if you are to enter the if-elseif-elseif-end sequence. This means you cannot reach the

 if isequal(time(i),off_tt)

test with equal values of time(i) and off_tt. Hence the 'isequal' test will always be false and k can never be incremented.

I am curious as to why you used 'isequal' at that point.  It is intended for testing equality between entire arrays and suggests that you may have meant something else in your code here.

Roger Stafford