[SciPy-user] Derivative() usage?

Robert Kern rkern at ucsd.edu
Thu Oct 21 12:15:03 CDT 2004


Francesc Alted wrote:
> Hi,
> 
> I'm trying to figure out how to compute the derivatives of a function with
> scipy, but the documentation is a bit terse for me:
> 
> def derivative(func,x0,dx=1.0,n=1,args=(),order=3):
>     """Given a function, use an N-point central differenece
>        formula with spacing dx to compute the nth derivative at
>        x0, where N is the value of order and must be odd.
> 
>        Warning: Decreasing the step size too small can result in
>        round-off error.
>     """
> 
> I would like to compute a derivative of an arbitrary order, but by reading
> the docs, I'm not sure what the n and order parameters exactly means.
> 
> Someone smarter than me can help me?

'n' as in d^n/dx^n .

Somewhat confusingly, 'N' is being used in the docstring as a synonym 
for 'order' and is the number of discrete points used to evaluate the 
numerical derivative. I'm going to fix that.

For example, when n=2, and order=3, one is computing the second central 
derivative using 3 points [x0-dx, x0, x0+dx].

-- 
Robert Kern
rkern at ucsd.edu

"In the fields of hell where the grass grows high
  Are the graves of dreams allowed to die."
   -- Richard Harter



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