What does the phrase "shift the calculus" mean in below paragraph:?

In addition to the coming Taiwan elections, the ratcheted-up tensions in the South China Sea—where the U.S. recently sent a patrol close to Chinese-built islands—have helped shift the calculus for Beijing. China’s and Taiwan’s claims in the South China Sea are identical—outlined on a line the shape of a cow tongue on a Kuomintang map.
http://www.wsj.com/articles/china-taiwan-summit-a-high-stakes-gamble-for-xi-jinping-ma-ying-jeou-1446645837

shift the calculus 在句中如何解釋?

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What does the phrase "shift the calculus" mean in below paragraph:?

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