Fix type errors in calc_rectilinear_lon_edge and calc_rectilinear_lat_edge in grid.py

[yantosca]

Name and Institution (Required)

Name: Bob Yantosca
Institution: Harvard + GCST

Describe the update

This PR fixes type errors in routines to compute the lon & lat edges of rectilinear grids (in gcpy/grid.py). Running this test program:

#!/usr/bin/env python3

import numpy as np
import gcpy

# Longitude parameters
lon_stride = 0.25
center_at_180 = True

# Latitude parameters
lat_stride = 0.3125
half_polar_grid = True

# Grid box lon & lat edges
lon_edge = gcpy.grid.calc_rectilinear_lon_edge(lon_stride, center_at_180)
lat_edge = gcpy.grid.calc_rectilinear_lat_edge(lat_stride, half_polar_grid)

# Grid box area
area = gcpy.grid.calc_rectilinear_grid_area(lon_edge, lat_edge)

print(f"Sum of global surface area [m2]: {np.sum(area)}")

currently results in these errors:

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/n/home09/ryantosca/test/python/grid.py", line 15, in <module>
    lon_edge = gcpy.grid.calc_rectilinear_lon_edge(lon_stride, center_at_180)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/n/home09/ryantosca/python/gcpy/gcpy/grid.py", line 981, in calc_rectilinear_lon_edge
    lon_edge = np.linspace(-180.0, 180.0, num=n_lon + 1)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/n/jacob_lab/Users/ryantosca/mamba/envs/test_env/lib/python3.12/site-packages/numpy/core/function_base.py", line 122, in linspace
    num = operator.index(num)


Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/n/home09/ryantosca/test/python/grid.py", line 16, in <module>
    lat_edge = gcpy.grid.calc_rectilinear_lat_edge(lat_stride, half_polar_grid)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/n/home09/ryantosca/python/gcpy/gcpy/grid.py", line 1026, in calc_rectilinear_lat_edge
    lat_edge = np.linspace(-1.0 * start_pt, start_pt,
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/n/jacob_lab/Users/ryantosca/mamba/envs/test_env/lib/python3.12/site-packages/numpy/core/function_base.py", line 122, in linspace
    num = operator.index(num)

This is because the num arguments that are passed to NumPy routine np.linspace within these routines are of type float rather than the expected int. The solution is to cast these to int.

Expected changes

After the fix, the program works as expected and prints

Sum of global surface area [m2]: 510065624779438.94

NOTE: These routines are not used in the benchmarking code but are user utilities.

Related Github Issue

• See How to replace ship emission in GEOS-Chem with my own data HEMCO#301

[lizziel]

Looks good to merge!