Making a point of data into matrix/vector form

my while loop for my every variable, n run ill get my i and therefore i got a few x and y coordinate in which when i use plot (x,y) they appear in dots only not in line how i make my graph into both dots and line?

Answer 1

[Star Strider]

You did not post any code, but this is not the first time this problem has presented here.

Subscript your ‘x’ and ‘y’ values in the loop, then plot them after the loop.

For example:

for k1 = 1:10
    x(k1) = k1.^2;
    y(k1) = 3 + 2*k1;
end
figure(1)
plot(x, y)
grid

Also, it is best not to use ‘i’ or ‘j’ as variables or loop counters in your code. MATLAB uses them for its imaginary operators, and using them as variables can be confusing.

[Victor Seaw]

oh codes ehm im sorry here:

a=-5;
b=5;

func =@(x) 4*x^3*2*exp(x)*cos(x);
x=3; % min segment
n=x+1;
z=0;
b=0;
while true
    hold on 
    plot(n,z,'r.')
    n=n+1
    i = CompTrap(func,a,b,n);

      if abs(i-z)<0.01
          break
      end
      z=i;
  hold off
  end

as you can see im trying to plot n and z but with my method im only getting points so im trying to get plots lines as well

[Victor Seaw]

because im doing this for the first section however when it comes to the second section where i need to plot a second data into my first graph im having problem since all of my codes are in point form.

[Star Strider]

I cannot run your code because I don’t have all the information.

However, this should work:

a=-5;
b=5;

func =@(x) 4*x^3*2*exp(x)*cos(x);
x=3; % min segment
n=x+1;
z=0;
b=0;
while true

      n=n+1
      N(n) = n;                   % <— ‘N’ AS ADDITIONAL VARIABLE
      i = CompTrap(func,a,b,n);

        if abs(i-z)<0.01
            break
        end
        z(n)=i;                   % <— ADD SUBSCRIPT (n)
  end

figure(1)
plot(N,z,'r-.')
grid

I added a variable ‘N’ to store the elements of ‘n’ (since it seems to be a counter, and I subscripted ‘z’. I don’t know where the subscripts begin, so you might instead want to store ‘z’ as:

z(n-x-1) = i;

so it begins at 1, keeping the array smaller.

Also, for this to work, your initial ‘x’ has to be such that ‘n’ is always an integer greater than zero. If not, it will crash, and you will have to introduce a separate counter.

[Victor Seaw]

it didnt stop after i run it

[Star Strider]

What do you mean? I don’t understand.

[Victor Seaw]

after i run the code that i added from you the loop wont stop i need to ctrl+c to force it to stop

[Star Strider]

Add ‘Z’ to store the ‘z’ values, then add ‘Z’ to the plot:

while true

      n=n+1
      N(n) = n;                   % <— ‘N’ AS ADDITIONAL VARIABLE
      i = CompTrap(func,a,b,n);

        if abs(i-z)<0.01
            break
        end
        z=i;
        Z(n) = z;                 % <— ADD ‘Z’ VECTOR
  end

figure(1)
plot(N,Z,'r-.')                   % <— CHANGE PLOT ARGUMENTS
grid

That should work.

[Victor Seaw]

it said vector must be same vector N having 26 column while Z having 25

[Victor Seaw]

the problem why im having that extra N is because:

while true

    n=n+1
    i = CompTrap(func,a,b,n);
      if abs(i-z)<0.01
          break
      end
      z=i;

end
as you can see when my abs(i-z)<0.01 it stops causing N to have an extra compare to Z

[Star Strider]

In that instance, move it to just above the ‘Z’ assignment:

while true

      n=n+1
      i = CompTrap(func,a,b,n);

        if abs(i-z)<0.01
            break
        end
        z=i;
        N(n) = n;                 % <— ‘N’ AS ADDITIONAL VARIABLE
        Z(n) = z;                 % <— ADD ‘Z’ VECTOR
  end

figure(1)
plot(N,Z,'r-.')                   % <— CHANGE PLOT ARGUMENTS
grid

Now, since they are both updated after the if block, they should have equal numbers of elements.

[Victor Seaw]

thanks and i used matrix addressing where N(1:end-1) in the plot which is more effective and less redundant because marks will be given on the most fastest way

[Star Strider]

My pleasure.

If my Answer solved your problem, please Accept it.