Function eir 

pub fn eir(
    voltage_v: Option<f64>,
    current_a: Option<f64>,
    resistance_ohm: Option<f64>,
) -> Result<EirResult, CalcError>

Calculate voltage, current, resistance, and power given any two of V, I, R.

Exactly two of the three options must be Some.

Errors

Returns CalcError::InsufficientInputs if fewer or more than two values are provided, or CalcError::OutOfRange if a zero denominator would result.