Why is symsum operator giving me this answer?

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Baldemy 2014-9-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/155807-why-is-symsum-operator-giving-me-this-answer

评论： Star Strider 2014-9-22

I am trying to find the sum of a series that goes like 20.^-20+19.^-19+...+1.^-1 Why is the answer such a massive number and why doesn't the formatting command work?

>> syms k

>> format shorteng

>> symsum(k.^(-1.*k),1,20)

ans =

32704926622076322328309250821720456282760440107801920978264646490630691318184399029563038640802578744801153948761512969045499776815021/25327407480969699779230080718754457246512673155164240823229977202846792179169322076528314293406963808740247706009600000000000000000000

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采纳的回答

Star Strider 2014-9-22

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/155807-why-is-symsum-operator-giving-me-this-answer#answer_152551

在 MATLAB Online 中打开

The Symbolic Math Toolbox has its own way of formatting numbers: the vpa function:

syms k
S = symsum(k.^(-1.*k),1,20);
S = vpa(S, 5)

produces:

S =
1.2913

You can of course set the number of digits to whatever you want.

Also see the digits and double functions.

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Baldemy 2014-9-22

Ok great I didn't see the "/" thanks a ton.

Star Strider 2014-9-22

My pleasure!

I didn’t see it either at first, the reason I used numden for the clarification.

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