TheAlgorithms/Python · error · ValueError

mobility cannot be negative

Error message

mobility cannot be negative

What it means

Thrown by electric_conductivity() when mobility < 0 while exactly one argument is 0. Carrier mobility mu (m^2/V*s) is non-negative by definition; a negative value would invert the sigma = n*e*mu relation, so it is rejected before the solver branches run.

Source

Thrown at electronics/electric_conductivity.py:52

        ...
    ValueError: mobility cannot be negative
    >>> electric_conductivity(conductivity=50, electron_conc=0, mobility=0)
    Traceback (most recent call last):
        ...
    ValueError: You cannot supply more or less than 2 values
    >>> electric_conductivity(conductivity=50, electron_conc=200, mobility=300)
    Traceback (most recent call last):
        ...
    ValueError: You cannot supply more or less than 2 values
    """
    if (conductivity, electron_conc, mobility).count(0) != 1:
        raise ValueError("You cannot supply more or less than 2 values")
    elif conductivity < 0:
        raise ValueError("Conductivity cannot be negative")
    elif electron_conc < 0:
        raise ValueError("Electron concentration cannot be negative")
    elif mobility < 0:
        raise ValueError("mobility cannot be negative")
    elif conductivity == 0:
        return (
            "conductivity",
            mobility * electron_conc * ELECTRON_CHARGE,
        )
    elif electron_conc == 0:
        return (
            "electron_conc",
            conductivity / (mobility * ELECTRON_CHARGE),
        )
    else:
        return (
            "mobility",
            conductivity / (electron_conc * ELECTRON_CHARGE),
        )


if __name__ == "__main__":

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass a positive mobility (electrons in Si at room temperature: ~0.135 m^2/V*s).
2. If mobility is the unknown, pass 0 for it and supply conductivity and electron_conc.
3. Sanity-check material parameter tables once at load time.

Example fix

# before
electric_conductivity(conductivity=50, electron_conc=1e21, mobility=-0.135)

# after
electric_conductivity(conductivity=50, electron_conc=1e21, mobility=0.135)

if mobility < 0:
    raise ValueError("mobility must be >= 0")
name, value = electric_conductivity(conductivity, electron_conc, mobility)

When it happens

Trigger: electric_conductivity(conductivity=50, electron_conc=0, mobility=-300) — valid zero-count but negative mobility.

Common situations: Typo'd minus signs in hand-entered material parameters; Hall-effect derivations producing signed 'effective' mobilities; unit tables copied with negative conventions.

Related errors

• Electron concentration cannot be negative in a semiconductor
• Hole concentration cannot be negative in a semiconductor
• Intrinsic concentration cannot be negative in a semiconducto
• Conductivity cannot be negative
• Electron concentration cannot be negative

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/e257959db7f2cb68. Report an issue: GitHub.