NSum
 Usage
Notes
 Further Examples
Here is an exact summation and an approximation to it.
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This gives a close approximation.
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Here is another exact summation and an approximation.
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Again NSum gives a close approximation.
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Using Options to Get Better Results Here is the exact value of a sum.
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Here is the approximate value of exact.
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Here is the approximation by NSum. The absolute error is about  times greater than the exact result.
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Using the option NSumTerms gives a much better result.
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Using the option NSumTerms with higher working precision gives an even better result.
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Changing the Method option and in addition using NSumExtraTerms gives a still better result.
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