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product ? *** and sum ? *** - Printable Version

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product ? *** and sum ? *** - Helge Gabert - 07-29-2014 05:22 AM

I just ran into this - -

in Home: product(N,N,1,3,.5) runs fine

But product(N,N,.5,3,.5) does not run and returns the arguments as multiplicands.

in CAS: product(n,n,1,3,1/2) runs fine

But again, product(n,n,1/2,3,1/2) returns 3/4*n^2.

It appears that the minimum value is not to be less than one, which is strange.


RE: product ? - Thomas Ritschel - 07-29-2014 11:19 AM

According to the manual the arguments (a, b, and p) should be integers:
Code:
product(Expr||Lst,[Var||Lst],[Intg(a)],[Intg(b)],[Intg(p)])

It turns out that the step size (p) could be non-integral, but a and b must be integers. Otherwise you'll get those "list products" (e.g. multiplication of all 5 arguments).


RE: product ? - Helge Gabert - 07-29-2014 03:35 PM

Apparently so. Maybe this requirement can be relaxed in the future, so that the product command becomes more useful.


RE: product ? - Thomas Ritschel - 07-29-2014 04:58 PM

Of course one could rewrite product(N,N,0.5,3,0.5) as product(N/2,N,1,6,1) and would get the correct answer (45/4).


RE: product ? - Helge Gabert - 07-29-2014 07:09 PM

Yes, that would be an easy one to transform.

Others won't be, however.


RE: product ? - parisse - 07-30-2014 03:43 PM

If arg3 and arg4 are not integers, product behaves like if you input a list of values, it makes the product of the elements of the list. I'm going to modify product:
- if the argument is a list (with [] or {} delimiters) or does not have 5 args, no change
- if the argument is a sequence with 5 arguments, do what you want


RE: product ? and sum ? - Helge Gabert - 07-31-2014 12:39 AM

Thank you. That would be great, and maybe we'll see that in the Prime, too!

[Edit: Actually, sum behaves similarly. Would it be possible to modify product and sum in the same way?]


RE: product ? *** and sum ? *** - parisse - 07-31-2014 07:42 AM

There is nothing to do for that, since it's in the common code product and sum share.


RE: product ? *** and sum ? *** - Helge Gabert - 07-31-2014 03:24 PM

OK, thanks for replying!