[SciPy-user] Derivative() usage?

David Grant david at dwavesys.com
Wed Nov 3 17:38:53 CST 2004


Robert Kern wrote:

> Giovanni Samaey wrote:
>
>>
>>>
>>> '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].
>>
>>
>>
>> Normally, one would expect "order" to be an indication of the 
>> accuracy of the derivative.  So, order=p should mean
>> d^n/dx^n (exact answer) - (what's computed) = O(dx^p) where dx is the 
>> mesh spacing.
>> Clearly, with three points for the second derivative, the order is 
>> only two, so this is clearly not a mathematically correct use of the 
>> word "order"...
>
>
> Not really. "Order" is an incredibly overloaded word in this area. Its 
> usage here is one of several acceptable ones. "numpoints" may be 
> clearer, though.
>
Where is the derivative function in scipy?



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