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Inductor Current & Stored Magnetic Energy

Calculate stored energy in a linear ideal inductor from positive inductance and signed current.

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A 2 H inductor carrying 3 A stores 9 J. Reversing current to −3 A leaves stored energy at 9 J.

Stored magnetic energy = ½LI²

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This is an ideal component model. Losses, tolerances, temperature dependence, parasitics and component ratings require separate information.
Inductance must be positive and stored energy nonnegative. Current may have either sign; zero current gives zero stored energy.
The model assumes constant linear inductance. Saturating or nonlinear magnetic components require an appropriate flux-linkage relationship.
Solving current from energy returns its nonnegative square-root branch. Energy alone does not identify current direction. Zero current and energy do not determine inductance.

At fixed inductance, stored energy increases fourfold.

No. Current is squared, so either direction produces the same nonnegative energy at equal magnitude.

Bookify requires positive inductance and nonnegative stored magnetic energy, while allowing signed current.