# I Numerical derivative

1. Jan 14, 2017

### ddddd28

Hello,
What is the numerical formula for a derivative, considering the x's are not in the same distance?

2. Jan 14, 2017

### Staff: Mentor

What do you mean by "numerical formula for a derivative" and which "x's" at which distances?

Do you have a discrete approximation for a function and try to approximate its derivative? There are multiple ways to do this, and the best one will depend on the application.

Please stop making even more copies of this thread! I deleted the copies.

3. Jan 14, 2017

### Svein

The best you can do is obviously $f'(x_{n})\approx \frac{y_{n+1}-y_{n}}{x_{n+1}-x_{n}}$.

There are better formulas, but then you have to know more about the distribution.

NB! Be very careful with numerical derivation of measurement data! Very often you subtract the significant part of the data and end up with the "noise" inherent in the data.