# Wikipedia:Reference desk/Archives/Mathematics/2014 June 14

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# June 14

## Euler characteristic in nonwestern sources

Does the Euler characteristic or anything like it appear in any of the nonwestern schools of mathematics (Chinese, Arabic, etc)? Euler characteristic doesn't mention anything nonwestern, but it mentions almost nothing of the history anyway. Staecker (talk) 00:32, 14 June 2014 (UTC)

This is probably an undecidable problem. Bo Jacoby (talk) 11:41, 14 June 2014 (UTC).
Although still western, a version of the Euler characteristic was independently discovered by Descartes long before Euler (see http://www.ams.org/samplings/feature-column/fcarc-eulers-formula). Sławomir Biały (talk) 12:24, 14 June 2014 (UTC)

## Exchange rates

How are currency exchange rates set? Is there a specific formula which is used? I can't find any articles on it. Clover345 (talk) 15:32, 14 June 2014 (UTC)

In general, you have a floating exchange rate, and the market dictates the exchange rate, much as it dictates stock prices. So, for example, if you try to sell your flurbles for 10 ricktovers each, and nobody will buy them at that price, you might try to sell them at a lower exchange rate, until you get a buyer. In this way the rates are set.
There are occasional fixed exchange rates, where the governments of one or more nations sets a certain exchange rate with the currency of another. Here they do use a formula, perhaps as simple as 1 flurble = 1 ricktover, or maybe 1 flurble = 1.5 ricktovers until the end of the year, then 1 flurble = 2 ricktovers after that. However, market forces often overwhelm the ability of a government to maintain fixed rates, in the long term, as it requires buying and selling lots of currency to keep the price steady, and that gets expensive. You can think of it like building a dam to keep water contained, it will only be contained for so long, then a storm will come along and the dam will burst. When a given fixed exchange rate can no longer be held, they may set a new, more realistic fixed exchange rate, but eventually that will fall too, resulting in what is really a stepped floating currency. Or they can just allow the currency to float freely. StuRat (talk) 16:01, 14 June 2014 (UTC)
Fixed exchange rates were usual under the Bretton Woods system at the end of World War Two until the 1970s, in which the dollar was fixed against gold and other currencies were fixed against the dollar. When there was too much selling of one currency, such as the British pound, against the dollar, the government would have to devalue its currency. In the 1970s, fixed exchange rates for major industrial currencies were abandoned and floating exchange rates implemented. As was said above, floating exchange rates use the free market, as the stock market does. Robert McClenon (talk) 17:05, 14 June 2014 (UTC)
You might do better to ask what phenomena affect exchange rates! —Tamfang (talk) 21:37, 14 June 2014 (UTC)
That question would be better off at the economics Reference Desk. Robert McClenon (talk) 21:01, 15 June 2014 (UTC)
Ha ha. —Tamfang (talk) 07:59, 16 June 2014 (UTC)