dgraph-io/dgraph · error

Fractional power of negative number

Error message

Fractional power of negative number

What it means

ErrorFractionalPower is a sentinel error in Dgraph's math package returned by applyPow when a negative base is raised to a fractional exponent, which has no real-valued result. Dgraph does not return complex numbers, so the operation is rejected.

Source

Thrown at query/math.go:29

	"github.com/golang/glog"
	"github.com/pkg/errors"

	"github.com/dgraph-io/dgraph/v25/types"
)

type mathTree struct {
	Fn    string
	Var   string
	Const types.Val // If its a const value node.
	Val   *types.ShardedMap
	Child []*mathTree
}

var (
	ErrorIntOverflow     = errors.New("Integer overflow")
	ErrorFloat32Overflow = errors.New("Float32 overflow")
	ErrorDivisionByZero  = errors.New("Division by zero")
	ErrorFractionalPower = errors.New("Fractional power of negative number")
	ErrorNegativeLog     = errors.New("Log of negative number")
	ErrorNegativeRoot    = errors.New("Root of negative number")
	ErrorVectorsNotMatch = errors.New("The length of vectors must match")
	ErrorArgsDisagree    = errors.New("Left and right arguments must match")
	ErrorShouldBeVector  = errors.New("Type should be []float, but is not. Cannot determine type.")
	ErrorBadVectorMult   = errors.New("Cannot multiply vector by vector")
)

// processBinary handles the binary operands like
// +, -, *, /, %, max, min, logbase, dot
func processBinary(mNode *mathTree) error {
	aggName := mNode.Fn

	mpl := mNode.Child[0].Val
	mpr := mNode.Child[1].Val
	cl := mNode.Child[0].Const
	cr := mNode.Child[1].Const

View on GitHub (pinned to 759e242be6)

Solutions

1. Guard the base with abs(): math(abs(x) ^ 0.5) if sign is irrelevant
2. Filter out negative bases before the math block using @filter(ge(x, 0))
3. Use an integer exponent when working with negative bases

Example fix

// before
math(x ^ 0.5)
// after
math(abs(x) ^ 0.5)

// Filter non-negative bases before pow:
// { q(func: type(M)) @filter(ge(x, 0)) { r as math(x ^ 0.5) } }
const query = `{ q(func: type(M)) @filter(ge(x, 0)) { r as math(x ^ 0.5) } }`;

try {
  const res = await dgraph.newTxn().query(query);
} catch (e) {
  if (String(e).includes('Fractional power')) {
    // retry with math(abs(x) ^ exp)
  } else throw e;
}

When it happens

Trigger: math(a ^ b) where a < 0 and b is non-integral (e.g. math(x ^ 0.5) on negative x); returned by applyPow.

Common situations: Taking fractional roots (sqrt, cube root) of signed data that can be negative; using pow on normalized values that dipped below zero due to upstream bugs.

Related errors

• Integer overflow
• Float32 overflow
• Division by zero
• Log of negative number
• Root of negative number

AI-assisted analysis of dgraph-io/dgraph@759e242be6 (2026-09-01). Data as JSON: /api/errors/7e162034a616175e. Report an issue: GitHub.