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what is the meaning of the "alias erro"

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Old   February 23, 2006, 11:22
Default what is the meaning of the "alias erro"
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ztdep
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Hello:

what is the meaning of the 'alias erro" in the spectral method!

regards
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Old   February 23, 2006, 12:12
Default Re: what is the meaning of the "alias erro"
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scar
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"alias erro" sounds like "aliasing error". An aliasing error can be seen as a contamination of the high modes that are not solved. An good reference is Canuto et al. Spectral methods in fluid mechanics
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Old   February 25, 2006, 00:50
Default Re: what is the meaning of the "alias erro"
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Wen
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The simples explanation is like this:

For example when you look at a fan spinning fast. You sometimes see a slowly rotating pattern, or even a slow rotation to the counter direction. And you are sure you the fan isn't spinning that slowly. So should you believe your eyes? The answer is no. Becasue your eyes has a limited response quickness, i.e. it takes at least 0.01 sec for you to form the image in your brain after you actually see the fan at location A. That means your eyes has low resolusion than necessary, or you can only reslove maximum frequency of 1/0.01 =100. If the fan is rotating at a speed faster than that, your measurement only show you a frequency smaller than 100. Hence the fast mode is aliased to (mapped to) the slow mode. And you will be interpreting a faster(high freq) motion as being a slow (low freq) mothion. If a system has both high freq and low freq at the same time. And your resolution is in the middle, then, you will see two low freq motions. That means the correct low freq motion is contaminated by the aliased (wrongly measured) high freq motion and the high freq motion is completely lost.

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Old   February 26, 2006, 12:11
Default Re: what is the meaning of the "alias erro"
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ztdep
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thank you very much! your are a genius.

i have understood it !
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