Fwd: [Numpy-discussion] Re: inconsistent use of axis= keyword argument?

Alan G Isaac aisaac at american.edu
Sat Feb 25 13:25:06 CST 2006


On Sat, 25 Feb 2006, Nils Wagner apparently wrote: 
> Is it possible to use aliases for these operators ? 
> In textbooks (Matrix Algebra by Abadir and Magnus, 
> Cambridge University Press (2005)) you will find 
> The vec-operator transforms a matrix into a vector by 
> stacking its columns one underneath the other. 

At http://www.american.edu/econ/pytrix/pyGAUSS.py
you will find these vec operations
(as GAUSS "look alikes").

hth,
Alan Isaac

#vec: vectorize columns of 2-D array
# Format:    y = vec(x)
# Input:     x        RxK 2-D array (or matrix)
# Output:    y        (RK)x1 2-D array:
#                       stacked columns of x
# Remarks:   ravel OK for non-contiguous arrays
# Author: Alan G Isaac (aisaac AT american DOT edu)
# Date:   20050420
def vec(x):
	assert(len(x.shape)==2), "For 2-d arrays only."
	return x.transpose().ravel().reshape((x.size,-1))

#vecr: vectorize rows of 2-D array
# Format:    y = vecr(x)
# Input:     x        RxK 2-D array (or matrix)
# Output:    y        (RK)x1 2-D array:
#                       stacked rows of x
# Remarks:   ravel OK for non-contiguous arrays
# Author: Alan G Isaac (aisaac AT american DOT edu)
# Date:   20050420
def vecr(x):
	assert(len(x.shape)==2), "For 2-d arrays only."
	return x.ravel().reshape((x.size,-1))







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