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Inverse DFT Calculator

Inverse DFT x[n]=(1/N) Σ X[k] e^{2πi kn/N}, N≤64, Numpy backward. Same engine as Discrete Fourier Transform. Radix-2 FFT is on /fft. Not Laplace. Runs locally.

Instant result
Result
—

Enter values to calculate.

Inputs—
Mode—
Formula—
Trust summary Engine tested · Specification checked · 17/17 tests · Production surface contract 3/3 · v1.2.0
Input interpretation
Enter values to calculate.
Result
—
Model
Numpy-backward inverse DFT of a length-N sequence, N≤64.
Scope
Mode locked to idft
Verification
Engine tested · 17/17 tests · Production surface contract 3/3 · Specification checked · v1.2.0
Named expert review
Optional · Not performed
Specification basis
  • ISO 80000-2:2019 Quantities and units — Mathematics
Specification basis
Evidence
6 golden · 3 boundary · 8 property · Production surface contract 3/3 · Artifact integrity PASS
Production
Embedded snapshot: unpublished · Build schema 1.2.0 ready · Semantic contract ✓ · Attestation report not published on origin · Live production status STALE (2 capabilities; 162 remain CURRENT) @ 2026-09-20T09:01:12.147Z
Semantic contract
PASS

Formulas

Core equations used by this calculator.

Inverse DFTx[n] = (1/N) Σ_k X[k] e^{2πi kn/N}
DCX = [N, 0, …, 0] → x = [1, 1, …, 1]
iSame engine as /discrete-fourier-transform. The 1/N scale is here, not on the forward transform. Not a second engine. Radix-2 FFT is on /fft.

How to use

1

Enter X[k] as samples

Real list, optional im of the same length. N must be 1–64. Default 4,0,0,0.

2

Read x[n]

DC spectrum 4,0,0,0 inverts to 1,1,1,1. Round-trip with /dft recovers the sequence.

Example calculations

Common configurations with formula and result.

ϟ

Inverse DC

samples = 4,0,0,0

x = [1, 1, 1, 1]
1
ϟ

Inverse all-ones

samples = 1,1,1,1

x = [1, 0, 0, 0]
1

Inverse DFT calculator specification

Version 1.2.0 · Engine tested

Calculation status

Review policy · Evidence

Definition
The Numpy-backward inverse DFT is x[n]=(1/N) Σ_k X[k] e^{2πi kn/N}. This page is mode=idft on math.transform.dft. Direct O(N²), N≤64. Forward DFT lives on the sibling discovery URL. Not FFT. Not Laplace. Not CAS.
What it calculates
Numpy-backward inverse DFT of a length-N sequence, N≤64.
Inputs
  • samples
  • im?
Outputs
  • n
  • re
  • im
  • mag
Formula
x[n] = (1/N) Σ_k X[k] e^{2πi kn/N}
Assumptions
  • Mode locked to idft
  • Direct O(N²), N≤64, Numpy backward 1/N
  • Not this page's FFT — radix-2 is on /fft
  • Not Laplace, not CAS
Units
  • dimensionless
Boundary conditions
  • empty samples → INVALID_INPUT
  • N > 64 → INVALID_INPUT
  • unknown mode → INVALID_MODE
Example
samples=4,0,0,0 → x=[1,1,1,1]
Validation cases

2 published on this page · 17/17 tests · Production surface contract 3/3 · View evidence

  • samples=4,0,0,0 → re=[1,1,1,1]
  • mode=laplace → INVALID_MODE
Specification basis
  • ISO 80000-2:2019 Quantities and units — Mathematics
Calculation version
1.2.0

Other calculators in this family: Bessel I Calculator, Bessel J Calculator, Bessel K Calculator, Bessel Y Calculator, Beta Function Calculator, Brent Method Calculator, Definite Integral Calculator, DFT Calculator . Explore all Numerical Calculus.

→ Bessel I Calculator I_n(x) for integer n=0…8. Same engine as Special Functions. Not W_{-1}. Not CAS. Runs locally. › → Bessel J Calculator J_n(x) for integer n=0…8. Same engine as Special Functions. Not W_{-1}. Not CAS. Runs locally. › → Bessel K Calculator K_n(x) for integer n=0…8 and x>0. Same engine as Special Functions. Not W_{-1}. Not CAS. Runs locally. › → Bessel Y Calculator Y_n(x) for integer n=0…8 and x>0. Same engine as Special Functions. Not W_{-1}. Not CAS. Runs locally. › → Beta Function Calculator Complete Euler B(x, y) = Γ(x)Γ(y)/Γ(x+y) for x>0, y>0. Same engine as Special Functions. Not incomplete beta. Not CAS. Runs locally. › → Brent Method Calculator Brent’s method (golden section plus inverse parabolic interpolation) for a minimum of a polynomial, sin, or exp on [a, b]. Same engine as One-Dimensional Optimization. Not root-finding Brent. Runs locally. › → Definite Integral Calculator Composite trapezoid, Simpson 1/3, or Gauss–Legendre of a polynomial, sin, or exp on [a, b]. Not indefinite symbolic integrate. Runs locally. › → DFT Calculator Forward DFT X[k]=Σ x[n] e^{−2πi kn/N}, N≤64, unnormalized. Same engine as Discrete Fourier Transform. Radix-2 FFT is on /fft. Not inverse, not Laplace. Runs locally. ›
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Frequently asked questions

Key distinctions behind the calculation.

Is this a second DFT engine?

No. It is mode=idft on math.transform.dft, the same engine as /calc/math/discrete-fourier-transform.

Why 1/N here?

Numpy backward puts the 1/N scale on the inverse. The forward DFT on /dft is unnormalized.

Where does this run?

Locally in the browser by default. REST and MCP call the same discrete-fourier-transform engine.