Added test script for np.nonzero()

[tejalbarnwal]

added following script at ulab/tests/2d/numpy/nonzero.py

try:
   from ulab import numpy as np
except:
   import numpy as np

array = np.array(range(16)).reshape((4,4))
boolean_array = array < 3

# np.nonzero() returns a tuple of corresponding row and column 
# indices array for each element being true in boolean array
row_indices, column_indices = np.nonzero(boolean_array)

print("Given Array:\n", array)
print("\nBoolean Array:\n", boolean_array)
print("\nFollowing indices have non-zero values:")
for i in range(len(row_indices)):
    print("row", row_indices[i], "and column", column_indices[i])

The expected output file is located at ulab/tests/2d/numpy/nonzero.py.exp Expected output:

Given Array:
 array([[0.0, 1.0, 2.0, 3.0],
       [4.0, 5.0, 6.0, 7.0],
       [8.0, 9.0, 10.0, 11.0],
       [12.0, 13.0, 14.0, 15.0]], dtype=float64)

Boolean Array:
 array([[True, True, True, False],
       [False, False, False, False],
       [False, False, False, False],
       [False, False, False, False]], dtype=bool)

Following indices have non-zero values:
row 0 and column 0
row 0 and column 1
row 0 and column 2

[v923z]

nonzero works with arrays of arbitrary dtype, so e.g., this is also valid:

>>> a = np.array(range(9), dtype=np.uint8).reshape((3,3)) - 4
>>> print(np.nonzero(a))

You can simply loop through the types like in https://github.com/v923z/micropython-ulab/blob/master/tests/2d/numpy/arange.py. Would you mind adding this, so that the test would be complete?

[tejalbarnwal]

sure, I will update with this

[v923z]

sure, I will update with this

OK, thanks! Let me know when are ready. The rest of the PR is done, so as soon as you can update your test script, we could merge this into master.

[tejalbarnwal]

I have updated the script to loop through different data types

[v923z]

Fantastic! Many thanks for sticking with it till the very end! I hope you enjoyed the ride, and I am looking forward to your future contributions.

[tejalbarnwal]

Yes, sure