Why is symsum operator giving me this answer?

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

Answer 1

[Star Strider]

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.

[Star Strider]

Baldemy’s Answer moved here:

Thanks for the quick answer. So that huge answer I got was actually a tiny number?

[Star Strider]

My pleasure!

It’s actually a fraction, as can be demonstrated by:

[Sn, Sd] = numden(S)

where Sn and Sd are the numerator and denominator respectively.

The vpa function turns it into a decimal fraction.

[Baldemy]

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

[Star Strider]

My pleasure!

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