Plotting with a for loop

I am trying to plot this equation with for loop for x values between -3 and 6; y = x^4 - 4*x^3 - 6*x^2 + 15.

I am including the code and the plot that I get, why is my plot looking like this and how can I fix it?

for i = 1:10
    
    x(i)= i-4;
    y(i) = (i-4)^4 - 4*(i-4)^3 - 6*(i-4)^2 + 15;
    
   
end

plot(x,y)

[jessupj]

i think you have extra values of x and y that are not 'in the loop'.

try

plot(x(1:10),y(1:10))

fyi, matlab is 'built' to do this kind of thing without any explicit loops:

x = -3:6;  % or -3:0.5:6 if you want half-integer steps between points
y = x.^4 - 4.*x.^3 - 6.*x.^2 + 15;
plot(x,y)

you need the extra '.' in multiplication and exponentiation to tell matlab to perform the operations element-wise on the vector.

[Rik]

@Jussupj: you should move that to the answer section, because counting the points in the graph a missing pre-allocation is indeed causing this.

(and you would also need the dot for the division operation)

[German Bravo]

Thank you, both ways work, adding the '.' in multiplicatin and exponentiation is very useful.

Also I cleared the workspace and that worked as well.

[Isiah Pham]

At the beginning of every script you should always put "clear;close;clc" to get rid of variables and such when you run things.

If you add more points your graph would also look smoother and more like the equation.

[Rik]

You should not use them as a habit. During debugging it is a good idea (especially clear), but you should always keep thinking.

• only use clc if you are printing things to the command window
• only use clear (or clearvars) if you are not preallocating all your variables
• only use close if you are actually opening new figures