[Numpy-discussion] Calculating roots with negative numbers

[Matthias Hillenbrand]

Hello,

I want to calculate the root of a numpy array with negative numbers.
Here is an example:

x = linspace(-10,10,100)
h = zeros(100)

h[where(abs(x) < 2)]  = sqrt( abs(x) -2 )
h[where(2 <= abs(x))]  = 1j * sqrt( 2 - abs(x) )

Unfortunately I get the following error:     Warning: invalid value
encountered in sqrt
and h contains some NaN-values

How can I make a correct case differentiation in combination with
roots that might contain negative values?

Thank you very much,

Matthias