Writing if function to Plot graph?

So I have to write a script that creates a vector with x =1 :35 and then evaluates tusing an if statement

 y(x)={2 if x<6 ,(x-4) if 6=<x<20,(36-x) if 20=<x+,35}

which then plots y against x and calculates the min and max values of the curve.

What I have written is this:

x = 1:35 ; 
for y=(x)
if x < 6
x=2;
  elseif x>=6
      then x = (x-4);

    elseif x>=20 
    then x = (36-x)

 end
  end
  plot(y,x)

however it doesn't really plot anything.

Can anyone show me where I have gone wrong at all?

Thanks

[Rik]

I would recommend a crash course. There are several free online tutorials you can do.

The loop index in the for-loop is not used, therefore y is 35 by definition and x=2. If you change it around, you would get errors, because Matlab doesn't use then as a key word.

Morale of the story: don't do this with a loop. Do this with logical indexing.

Answer 1

[KL]

You have tried something but you have got very few things wrong. Firstly when they say

y(x)={2 if x<6 ,
     (x-4) if 6=<x<20,
     (36-x) if 20=<x+,35}

it means, y takes different values based on x and not x should be reassigned.

You have created x rightly in the beginning with the following line

x = 1:35;

Next you just need to calculate different y inside a for loop. To do that, just have a look at the documentation of for loop

https://www.mathworks.com/help/matlab/matlab_prog/loop-control-statements.html

Anyway, simple idea is,

for x
  if x<6
     %y(x) = ..
  elseif x>=6 && x<20  %here you see, two conditions in the same line
     %your y
  else %since that convers the remaning possible x
     %y(x)= ...
  end
end

then finally plot using plot command

https://www.mathworks.com/help/matlab/ref/plot.html

plot(x,y)

Answer 2

[jean claude]

you can use this code

y=zeros(35,1);
for x = 1:35
 if x < 6
y(x)=2;
  elseif 6<= x && x<20
      y(x)= x-4;
    elseif x>=20 
    y(x)=36-x;
 end
end
x=1:35;
plot(x,y)