Concept

Minimum distance

The smallest number of places in which two different codewords of a code disagree.

Named by 3 essays across one field — each of them below, with the objects they name alongside it.

0000010100111001011101112 codewords in the 3-cube, minimum distance 3 — 1 error corrected, 2 detectedthe 2 balls of radius 1 hold 4 words each and cover all 8 exactly once: the code is perfect

Distance is a picture

A message is a corner of a cube and an error is a step along an edge. Everything a code can do is decided by how far apart the corners it uses are — and that is a fact about a drawing.

computation · error correcting codes
four data bits, three parity bitsdataparityweight00000000000101130010110300111014010011140101100301100013011101041000101310011104101001141011000311000103110100141110100411111117sixteen codewords of length seven, minimum distance 3 — measured over all 120pairsweights: 1×0 · 7×3 · 7×4 · 1×7, and the lightest non-zero one weighs 3

Sixteen spheres that fill a cube

A hundred and twenty-eight seven-bit words, sixteen of them chosen, and a ball of eight around each. Sixteen times eight is a hundred and twenty-eight exactly — so the balls tile the space with nothing left over, and the code wastes nothing at all.

computation · error correcting codes
012345678910012345678910sentf(0) = 4f(1) = 8f(2) = 7f(3) = 1f(4) = 1f(5) = 7f(6) = 8the message 4, 1, 3 read as 3x² + 1x + 4 over GF(11), evaluated at x = 0…6all 35 ways of keeping 3 of the 7 values were interpolated and every one returned the message

A polynomial through the gaps

Write the message as the coefficients of a polynomial and send its values instead. Any k of them determine the polynomial, so it does not matter which ones are lost — and it does not matter how many, as long as k survive.

computation · error correcting codes

Named alongside it

The objects these essays reach for when they reach for this one.

Error correcting codeHamming distanceSphere packing boundCheck digitCode rateCosetCounting argumentErasureFinite fieldHamming codeHypercubeInterpolation

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