MATLAB crashed when invoking symsum

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Maristie
Maristie el 4 de Mayo de 2017
Comentada: Maristie el 9 de Mayo de 2017
The minimal example:
symsum(log(nchoosek(100, x)), x, 0, 100)
I've got the sum using `for` statement just in less than 1s.
But when it comes to symsum, MATLAB just crashes.
I've tried this code both on my own machine (Debian 9.0, R2016b) and MATLAB online, but results are just the same.
Could you please help me out?
Thanks!

Respuesta aceptada

Wilson A N
Wilson A N el 9 de Mayo de 2017
This is probably because 'symsum' is trying to find some closed expression as an answer and it is unable to do so. If you use 'sum', it will try this out numerically and hence doesn't give an error. You can maybe try out the following command:
>>sum(subs(log(nchoosek(100, x)), x, 0:100))
  2 comentarios
Walter Roberson
Walter Roberson el 9 de Mayo de 2017
Right. symsum() should only be used if you are trying to find a formula for the summation, not if you just want to add a number of terms together. To add terms together, generate the list of terms and sum() them, the way Wilson A N shows.
Maristie
Maristie el 9 de Mayo de 2017
Thanks! It works!

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