Symbolic binomial coefficients?

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Alasdair
Messages : 2
Inscription : dim. avr. 19, 2020 1:17 am

Symbolic binomial coefficients?

Message par Alasdair » lun. avr. 20, 2020 1:06 am

Hello,

Does Xcas support binomial coefficients with symbolic parameters? The command "binomial(x,3)" produces the output

1/6 * x!/(x-3)!

which is true, but what I want is the polynomial x(x-1)(x-2)/6. I've tried taking the output of that binomial command and running expand, factor, collect, none of which helped. I also tried "unapply(binomial(x,3),x)" which didn't work either.

Or is there another command which will produce the output I want?

Thanks very much,
Alasdair

PS. Also, do these forum boards have the facility of including typeset mathematics?

parisse
Messages : 5082
Inscription : mar. déc. 20, 2005 4:02 pm
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Re: Symbolic binomial coefficients?

Message par parisse » lun. avr. 20, 2020 6:21 am

Alasdair a écrit :
lun. avr. 20, 2020 1:06 am
Hello,

Does Xcas support binomial coefficients with symbolic parameters? The command "binomial(x,3)" produces the output

1/6 * x!/(x-3)!

which is true, but what I want is the polynomial x(x-1)(x-2)/6. I've tried taking the output of that binomial command and running expand, factor, collect, none of which helped. I also tried "unapply(binomial(x,3),x)" which didn't work either.
You must call simplify here. More precisely factor(simplify(binomial(x,3))), because factor does not pre-simplify factorials.
PS. Also, do these forum boards have the facility of including typeset mathematics?
Unfortunately no. I've seen some links about latex plugins, but not maintained.
But you can include typeset maths inside Xcas for Firefox sessions, with $...$ (simple support, works offline) or more complete latex support with $$...$$ (does not work offline since mathjax support is required)
Examples (in French...): viewtopic.php?f=26&t=2514
viewtopic.php?f=26&t=2466

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