[Numpy-discussion] differencing numarray arrays.

[Robert Kern]

Mike Zingale wrote:

> Hi, I am trying to efficiently compute a difference of two 2-d flux
> arrays, as arises quite commonly in finite-difference/finite-volume
> methods.  Ex:
> 
> a = arange(64)
> a.shape = (8,8)
> 
> I want to do create a new array, b, of shape such that
> 
> b[i,j] = a[i,j] - a[i-1,j]
> 
> for 1 <= i < 8
>     0 <= i < 8

Try
b = a[1:] - a[:-1]

-- 
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