# How to plot polynomial function correctly?

103 views (last 30 days)
Adrian Brand on 24 Mar 2020
Hello, I'm trying to plot polynomial function but output is always bad. Can you help me find, what I'm missing? Thank you.
This is my code:
d = @(g)1-5*g-2.5*g.^2+6*g.^3+5*g.^4;
e = -2:1/100:2;
plot(e,d(e));
This is what I'm getting:
And this is what I want:

Alex Mcaulley on 24 Mar 2020
Your code is working fine, the difference is just the axis limits. Try this:
d = @(g)1-5*g-2.5*g.^2+6*g.^3+5*g.^4;
e = -2:1/100:2;
plot(e,d(e));
ylim([-2,5])
xlim([-3,6])

John D'Errico on 24 Mar 2020
Edited: John D'Errico on 24 Mar 2020
Hmm. Why does this feel like deja vu? (Answer: I just answered almost the same question for someone else, not 5 minutes ago.)
d = @(g)1-5*g-2.5*g.^2+6*g.^3+5*g.^4;
e = -2:1/100:2;
plot(e,d(e));
grid on
It looks fine to me. Whats the problem? That two programs arbitrarily chose a different set of axes to plot the same curve?
axis([-3,4.5,-1.5,4.5])
Same curve. Same plot. Very different conclusions, just by changing the axis scaling.
Adrian Brand on 24 Mar 2020
thank you very much too.
how do you plot the x axis?

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