TheAlgorithms/Python · error · ValueError

Inductance must be positive.

Error message

Inductance must be positive.

What it means

Thrown by charging_inductor() when inductance <= 0. Inductance appears in the exponent (-t*R/L); zero or negative L is non-physical for an RL charging model and would divide by zero or invert the curve, so it is rejected (last of three sequential guards).

Source

Thrown at electronics/charging_inductor.py:88

    ValueError: Source voltage must be positive.

    >>> charging_inductor(source_voltage=10,resistance=0,inductance=20,time=5)
    Traceback (most recent call last):
        ...
    ValueError: Resistance must be positive.

    >>> charging_inductor(source_voltage=15, resistance=25, inductance=0, time=5)
    Traceback (most recent call last):
        ...
    ValueError: Inductance must be positive.
    """

    if source_voltage <= 0:
        raise ValueError("Source voltage must be positive.")
    if resistance <= 0:
        raise ValueError("Resistance must be positive.")
    if inductance <= 0:
        raise ValueError("Inductance must be positive.")
    return round(
        source_voltage / resistance * (1 - exp((-time * resistance) / inductance)), 3
    )


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass inductance in henries as a positive number (e.g. 0.001 for 1 mH).
2. Validate unit conversion at your data boundary before calling.
3. Remember source_voltage and resistance already passed their checks when you see this error.

Example fix

# before
charging_inductor(source_voltage=15, resistance=25, inductance=0, time=5)

# after
charging_inductor(source_voltage=15, resistance=25, inductance=0.02, time=5)

if inductance <= 0:
    raise ValueError("inductance must be positive henries")
i = charging_inductor(source_voltage, resistance, inductance, time)

When it happens

Trigger: charging_inductor(source_voltage=15, resistance=25, inductance=0, time=5) or any negative inductance.

Common situations: Unit errors (mH/uH/nH vs H) collapsing to 0; forgetting to convert a datasheet value; passing a component count or tolerance percentage instead of henries.

Related errors

• Capacitance must be positive.
• Source voltage must be positive.
• Resistance must be positive.
• Capacitor at index {index} has a negative or zero value!
• You cannot supply more or less than 2 values

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/6467433aebcee2f6. Report an issue: GitHub.