How to test non-linearity of array (1x256 double)?

Can i check whether my array of size 1x256 double is a non linear or not.?

For example i have a following array A:

20 40 26 136 51 199 196 29 112 43 201 99 227 241 106 151 220 12 23 215

whether A is non linear or not? how to test the non linearity of A?

[KSSV]

What do you mean by non-linearity?

Fit a striaght line and get the regression between the data..is that okay with you?

Answer 1

[Walter Roberson]

Any vector which is not either constant or monotonically increasing or monotonically decreasing, cannot be linear.

If you consider a linear equation y = a*x + b, and take the derivative of it, y' = a, and take the derivative of that, y'' = 0 . So if you take diff(diff()) of your vector and the result is not 0 to within round-off error then you do not have a linear vector.