What's the error in my code?

I can't seem to plot this function I wrote. What is wrong with it? Thanks in advance!!

    function [] = Apple(D,T)

    x= linspace (0,30,3000);

    y=0;

    for i = 0:6;

      if x > (i*T) && x < ((T*i)+(D*T))

        y(x)= 1;

      elseif y(x) == 0;

      end

    end

    plot(x, y(x));

    ylim([-.25,1.25])

    end

[Matt J]

You forgot to describe what's not working, e.g., how to run it and any error messages it displays.

[Stephen23]

Please learn about vectorization !

Answer 1

[Michael Haderlein]

x > (i*T) && x < ((T*i)+(D*T))

You cannot use && in case of arrays. Use & instead.

if x > (i*T) && x < ((T*i)+(D*T))

You cannot use arrays as condition for the if structure. What should the program do if some elements of the array are true and some are false?

elseif y(x) == 0;

Again, that's an array as condition which doesn't work. Additionally, x is not an appropriate index (only values 1, 2, 3, and so on are allowed).

Answer 2

[Stephen23]

Here is a short list of some of the syntax errors and poor coding. Some of these prevent it from working:

1. MATLAB has one-based indexing . The code y(x) tries to obtain the zeroth element (as x(1)==0), which is invalid in MATLAB.
2. Logical short-circuit operators || and && require scalar logical values, not arrays as they are here: x > (i*T) && x < ((T*i)+(D*T)). Because x is an array, x>n will also be an array, and so the syntax x<n && ... will always be an error.

Others are just things that really could be done much much better:

1. Array preallocation before the loop: y probably needs to be defined to be the same size as x.
2. Pay attention to the editor code warnings : it shows one warning with the version I am using.
3. Variable name i should be avoided, as this is the name of the inbuilt imaginary unit .
4. The use of a for loop, when this simple code should really be vectorized .

Without knowing exactly what your aim is, it is hard to know how to "fix" this code, as it is very unclear.