symsum does not work with symprod

I'm trying to avaluate the following:

syms j k
double(symsum((-symprod((j+0.3-1)/(j), j, 1,k))^2, k, 2, Inf))

It returns: -0.0806, which is nonsensical, since this is a sum of squared numbers.

When I evaluate the same in Wolfram Alpha using "sum( (product (j+0.3-1)/j, j=1..k)^2, k, 2, infinity)", I get 0.226456, which seems to be correct, since Matlab seems to converge to this number up to k=100000 (and then it crushes). How can I make it work? Thanks.

Answer 1

[Walter Roberson]

syms j k
double(symsum((-symprod((j+0.3-1)/(j), j, 1,k))^2, k, 2, Inf))

ans = 0.2265

So it works in current releases.

I am checking back to see if I can figure out when it was fixed.

[Walter Roberson]

Works in R2019a, haven't tested R2018b yet.

[Walter Roberson]

Works in R2018b.

It appears that R2018a is the last release that has this problem.

It is a problem with the symsum() part, by the way; it is returning a hypergeom() minus a constant when it should be returning an expression in gamma() minus that same constant.

[Adam Golinski]

Walter, many thanks for your help. I've installed a new version and it works now indeed. Best wishes!