Is there any error in my code?

These are my codes to plot the graph of f(x, q) = (q^4/(q^3+6))(1+x^3)exp(-qx)

clear all
q = 0.4;
x = linspace(0,20);
for i = 1:length(x);
   f(i) = (q^4/(q^3+6))*(1+x(i))*exp(-q*x(i));
end
plot(x,f,'linewidth',2)
xlabel(x)
ylabel('f(x)')

please reply me with the correction. Thanks.

[Adam]

You are missing a ^3 from your code, but this really is something you should double-check yourself before asking other people!

You don't need a for loop either, you can just vectorise it, but if at the moment you are only at the level of for loops I will leave that aside.

You can also easily create a quick test script with correct results calculated by hand or by calculator to check whether your answer is right or not.

[Jan]

I've used the "{} Code" button to format your code, which was unreadable. Please do this by your own in the future - thanks.

Answer 1

[John BG]

Hi Lawrence

this is John BG ( <mailto:[e-mail] [e-mail]> )

even better, since you are after f(x,q) perhaps a 2D plot is more helpful

q = [0:.1:4];
x = linspace(0,20);
[Q,X]=meshgrid(q,x)
F = (Q.^4 ./ (Q.^3 + 6)) .* (1 + X.^3) .* exp(-Q .* X);
surf(F)

.

.

So Lawrence, if you find this answer useful would you please be so kind to consider marking my answer as Accepted Answer?

To any other reader, if you find this answer useful please consider clicking on the thumbs-up vote link

thanks in advance

John BG

<mailto:[e-mail] [e-mail]>

Answer 2

[Jan]

The ^3 in (1+x^3) has been forgotton:

... (1+x(i)^3) ...

You can do this without a loop also:

x = linspace(0,20);
f = (q^4 / (q^3 + 6)) * (1 + x.^3) .* exp(-q * x);