Shiwa and NGOpt give userwarnings if the budget is low

[lesshaste]

Both Shiwa and NGopt give a userwarning if the budget is below a certain level.

UserWarning: COBYLA: Invalid RHOEND; it should be a positive number and RHOEND <= RHOBEG; it is set to 1e-06
  warn(f'{solver}: Invalid RHOEND; it should be a positive number and RHOEND <= RHOBEG; it is set to {rhoend}')

For Shiwa this happens when budget < 60 and for NGOpt it happens when budget < 101.

Example code:

import numpy as np
import nevergrad as ng
from nevergrad.optimization.optimizerlib import Shiwa,NGOpt

def three_minima_function(params):
    x, y = params
    res = -2 * np.exp(-((x - 1) ** 2 + (y - 1) ** 2) / 0.2) - 1.5 * np.exp(-((x + 1) ** 2 + (y + 1) ** 2) / 0.5) - 1 * np.exp(-((x - 1) ** 2 + (y + 1) ** 2) / 1)
    res = np.ceil(res * 100) / 100
    return res

# Define the parameter space with bounds [-5, 5] for both x and y
parametrization = ng.p.Array(shape=(2,)).set_bounds(lower=[-5, -5], upper=[5, 5])

# Create the Shiwa optimizer
optimizer = NGOpt(parametrization=parametrization, budget=100)

# Run the optimization
recommendation = optimizer.minimize(three_minima_function)

# Get the optimal parameters and function value
optimal_params = recommendation.value
optimal_value = three_minima_function(optimal_params)

print(f"Optimal parameters: x = {optimal_params[0]:.6f}, y = {optimal_params[1]:.6f}")
print(f"Optimal function value: {optimal_value:.6f}")

Python 3.12.8
Ubuntu 24.04.2 LTS