how to allocate arrays in numba - numba

Question

I am trying to create an array inside numba jit function. I tried these two options and both return various errors
#njit
def monte_carlo_ou(T: int, nsamples: int = 100, dt:float=0.1, sigma_g:float =1.0, ):
particles = np.zeros(T, nsamples, dtype=float)
velocity_particles = np.zeros(nsamples , dtype=float)
return particles
monte_carlo_ou(100, 50, dt=0.1, sigma_g=1.0,)
TypingError: Cannot determine Numba type of <class 'numba.core.ir.UndefinedType'>
#njit
def monte_carlo_ou(T: int, nsamples: int = 100, dt:float=0.1, sigma_g:float =1.0, ):
particles = numba.float32[:, :]
velocity_particles = numba.float32[:]
return particles
monte_carlo_ou(100, 50, dt=0.1, sigma_g=1.0,)
Error :
TypingError: No implementation of function Function(<built-in function getitem>) found for signature:
getitem(class(float32), UniTuple(slice<a:b> x 2))
There are 22 candidate implementations:
- Of which 22 did not match due to:
Overload of function 'getitem': File: <numerous>: Line N/A.
With argument(s): '(class(float32), UniTuple(slice<a:b> x 2))':
No match.
During: typing of intrinsic-call at /var/folders/43/m_k444pn2z7c6ygxj0y3_c4r0000gn/T/ipykernel_58943/4011707724.py (6)
During: typing of static-get-item at /var/folders/43/m_k444pn2z7c6ygxj0y3_c4r0000gn/T/ipykernel_58943/4011707724.py (6)
Any advise on how to get started? All tutorials seems to be very limited

Answer 1

The problem is your first in-function line: the shape in np.zeros should be one tuple argument, not multiple scalar arguments.
particles = np.zeros(shape=(T, nsamples), dtype=float) worked for me.
shape= is not necessary but is explicit about how you should provide the shape of the array.