probsolve_ivp for ODE that is a function of t

[qing42102]

Describe the bug
If the ODE is a function of t, then probsolve_ivp gives the error TypeError: unsupported operand type(s) for -: 'float' and 'NoneType'. Upon further investigation, it turns out that t is passed in as None to the ODE function sometimes. Thus, this will give an error when performing any numerical operator on t. Is there something that I need to change in the ODE function to make it work when it's a function of t? I can post the entire traceback if needed.

To Reproduce

def stiff_ode(t, y):
    lambda_val = 2
    print(t)
    return lambda_val * y + np.exp(-t)

# Initial and final time value
t0 = 0.0
tmax = 1.0

# Initial condition
y0 = np.array([1])

sol = probsolve_ivp(stiff_ode, t0, tmax, y0, algo_order=2, adaptive=True, atol=1e-2, rtol=1e-2)

Expected behavior
There shouldn't be an error and t shouldn't be passed in as None to the ODE function.

System:

• Conda environment
• Python 3.10
• ProbNum 0.1.25
• NumPy 1.25