The field trace is the trace of multiplication by , equivalently the sum of its conjugates in a separable extension.
For a normal domain with fraction field , the field trace of an integral element in a finite separable field extension belongs to . Its conjugates are integral, so their sum is integral; it lies in and hence in by normality. This places the integral closure inside a trace-dual lattice.
For a finite field extension , the trace pairing is the bilinear form
It is nondegenerate exactly when is separable.
For a monic degree- polynomial over a commutative ring , let and let take the coefficient of in the reduced representative. The pairing is unimodular on : reversing one basis order gives a triangular matrix with diagonal ones. When embeds in a separable field extension, Lagrange interpolation identifies with . This yields the derivative formula for the inverse different.
For an -lattice in , its trace-dual lattice is
For the integral closure of , the trace dual is the inverse different.
For a nonzero fractional ideal of a number field, its trace-dual lattice is the fractional ideal
The equality follows from the definition of the inverse different and invertibility of fractional ideals. Under the positive metric on the Minkowski embedding of a number field, the Euclidean dual lattice of is : coordinatewise complex conjugation converts the positive inner product into the trace pairing. This assertion does not require that conjugation preserve the number field itself.
For the integral closure of a Dedekind domain in a finite separable extension, the discriminant ideal is locally generated by
where is a local -basis of . Intrinsically it is the image of under the determinant of the trace pairing.
The relative discriminant of a finite extension of number fields is the discriminant ideal of over . It satisfies
and its prime divisors are exactly the ramified finite primes.
The relative discriminant of a finite extension of number fields is the relative norm of a fractional ideal applied to its different ideal. Consequently, at ,
where is the residue-field degree and is the different exponent. Over , .
The trace form of a number field is the symmetric bilinear form
For nonzero , choose . Then
so the trace form is nondegenerate.
In a quadratic extension , an element is integral exactly when its relative trace and norm lie in .

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Field trace can refer to different concepts depending on the context, so I'll outline a few possible interpretations: 1. **General Definition**: In a broad sense, a field trace could refer to a record or representation of observations or data collected from a specific field or area of study. This could be used in various disciplines, such as ecology, geography, or even data science.