How do we determine as to how long we should sum an asymptotic series of a function to get the answer correct up to a particular precision?

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As an example, consider the asymptotic expansion for polygamma function . What should be the min value of 'k' in the equation to get the answer correct upto a particular precision, say pth. Is there a relation between p and k. Or is it simple trial and error?

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The accuracy of an asymptotic series depends on the series and its argument. Usually, the accuracy increases up to a point as more terms are taken. After this point, the accuracy decreases and the series eventually diverges.

A reasonable tactic is to add terms as long as they decrease in value and stop when they start increasing.