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Fix off-by-1 error in PageRank iteration limit (#452) 

If `findStationaryDistribution` is passed `0` as `maxIterations`, then
it should return the initial distribution.

Test plan: see new unit test

Paired with @wchargin
This commit is contained in:
Dandelion Mané 2018-06-29 14:01:17 -07:00 committed by GitHub
parent 4afa542422
commit a5608dd7c8
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GPG Key ID: 4AEE18F83AFDEB23
2 changed files with 13 additions and 6 deletions
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12
src/v3/core/attribution/markovChain.js
View File

@ -117,6 +117,12 @@ export function findStationaryDistribution(
} }
let iteration = 0; let iteration = 0;
while (true) { while (true) {
if (iteration >= fullOptions.maxIterations) {
if (fullOptions.verbose) {
console.log(`[${iteration}] FAILED to converge`);
}
return r0;
}
iteration++; iteration++;
const r1 = sparseMarkovChainAction(chain, r0); const r1 = sparseMarkovChainAction(chain, r0);
const delta = computeDelta(r0, r1); const delta = computeDelta(r0, r1);
@ -130,12 +136,6 @@ export function findStationaryDistribution(
} }
return r0; return r0;
} }
if (iteration >= fullOptions.maxIterations) {
if (fullOptions.verbose) {
console.log(`[${iteration}] FAILED to converge`);
}
return r0;
}
} }
// ESLint knows that this next line is unreachable, but Flow doesn't. :-) // ESLint knows that this next line is unreachable, but Flow doesn't. :-)
// eslint-disable-next-line no-unreachable // eslint-disable-next-line no-unreachable

7
src/v3/core/attribution/markovChain.test.js
View File

@ -182,5 +182,12 @@ describe("core/attribution/markovChain", () => {
const expected = new Float64Array([0.5, 0.5]); const expected = new Float64Array([0.5, 0.5]);
expectAllClose(pi, expected); expectAllClose(pi, expected);
}); });
it("returns initial distribution if maxIterations===0", () => {
const chain = sparseMarkovChainFromTransitionMatrix([[0, 1], [0, 1]]);
const pi = findStationaryDistribution(chain, {maxIterations: 0});
const expected = new Float64Array([0.5, 0.5]);
expect(pi).toEqual(expected);
});
}); });
}); });