The command where gives a useful construct that can take a Boolean array as a condition and either return the indexes of the array elements satisfying the condition or return different values depending on the values in the Boolean array.
The basic structure is:
where(condition, a, b)
This will return values from a when the condition is True and values from b when it is False.
For instance, consider a Heaviside function:
and its implementation with the command where:
def H(x):
return where(x < 0, 0, 1)
x = linspace(-1,1,11) # [-1. -0.8 -0.6 -0.4 -0.2 0. 0.2 0.4 0.6 0.8 1. ]
print(H(x)) # [0 0 0 0 0 1 1 1 1 1 1]
The second and third arguments can be either arrays of the same size as the condition (the Boolean array) or scalars. We'll give two more examples to demonstrate how to manipulate elements from an array or a scalar depending on a condition:
x = linspace...
