MATLAB crashed when invoking symsum

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!

Answer 1

[Wilson A N]

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))

[Walter Roberson]

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]

Thanks! It works!