Going up from negative in for loop counter

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Crista
Crista 2013-9-11
I'm trying to make this code
for x=-10:10;
y=-3*x^2;
end
plot(x,y)
Plot like this code
x=-10:10;
y=-3*x.^2;
plot(x,y,'--o')
I've tried
for x=-10:10
y(x)=-3*x.^2;
end
plot(x,y,'--o')
which doesn't work because I can't have the negative x numbers as y(x). I'm lost on how to fix this. Thank you.

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2013-9-11
编辑：Azzi Abdelmalek 2013-9-11
You can avoid using negative index
x=-10:10;
n=numel(x);
y=zeros(1,n) % Pre-allocate
for k=1:numel(x)
y(k)=-3*x(k)^2;
end
plot(x,y,'--o')

更多回答（1 个）

Mahdi
Mahdi 2013-9-11
When you plot, you`re only plotting the last point because the variable y is inside the for loop (and is not a matrix). Other than what`s been suggested, the way that you can do it is
for x=-10:10;
y=-3*x^2;
plot(x,y)
hold on
end
  1 个评论
Mahdi
Mahdi 2013-9-11
Please note that you should avoid for-loops to plot things like this because they`ll be resource-consuming.

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