braket an matrix in python
Parisa Ch wrote:
> h=[np.sort(np.abs(x-x[i]))[r] for i in range(n)]
> this is part of a python code. the last line is confusing? x is a matrix
> and x[i] is a number. how calculate x-x[i] for each i?
> why the put r in  ?
Brake it appart:
y = x - x[i] # the numpy feature that makes that possible is called
subtracts the value x[i] from every entry in the vector x
z = np.abs(y)
calculates the absolute value of every entry in y.
t = np.sort(z)
sorts the values in z and finally, assuming r is an integer,
u = t[r]
looks up a single scalar in the vector.
The enclosing "list comprehension" [expr for item in iterable] builds a list
of n values calculated as sketched above.