a better explanation of polyfit please

My teacher wants us to use polyfit and gave us a little bit of information on how to use it, but what he gave us makes no sense and I've looked on this website for an explanation and that didn't help me. I know that the form is polyfit(x,y,n) but I'm not sure what the n stands for or how to figure it out from a set of data. Thanks in advance.

Answer 1

[Star Strider]

The ‘n’ is the degree of the polynomial. The degree can be considered to be the highest power of the independent variable, x. So a first-degree polynomial is p(1)*x + p(2), a second-degree p(1)*x^2 + p(2)*x + p(3), and so forth.

[Savanna]

ahhh. So a follow-up question to your explanation is that I have this large row array and an equation that is to the 4th power(so 4th dregree), but when i use polyfit i only get NaN as the answers. why is that?

[Star Strider]

I don’t have your data or your code, so I can’t say why you are getting the NaN values.

If you have numbers in both your x and y vectors that have at least 6 elements in each and the same number of elements in both, none of which are NaN, and you fit them with a 4th-degree polynomial with polyfit, for instance:

p = polyfit(x, y, 4);

you should get numeric values for all elements of ‘p’, none of which are NaN.