Plotting with a for loop
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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)
5 个评论
jessupj
2020-5-7
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
2020-5-7
@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
2020-5-7
Isiah Pham
2020-5-8
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
2020-5-9
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
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2020-5-7
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