import math

f = lambda x, a, b, c, d: a / (1 + math.exp(-b - c * x - d * x**2))

def calc_and_save(a, b, c, d, filename="results.txt"):
    if a <= 0 or b <= 0 or c <= 0 or d <= 0:
        raise ValueError("Все параметры должны быть положительными")
    
    xs = list(range(-20, 21, 2))
    values = [f(x, a, b, c, d) for x in xs]
    
    with open(filename, "w", encoding="utf-8") as file:
        for i in range(0, len(values), 3):
            chunk = values[i:i+3]
            line = " ".join(f"{v:.6f}" for v in chunk)
            file.write(line + "\n")
    
    return xs, values