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Collecting coefficients of derivatives

asked 2017-07-10 16:41:23 +0200

Ursula gravatar image

I have a complicated expression involving derivatives of a function, and I'd like to collect all of the first, second, third, etc. derivatives. For example, my expression starts:

a1*a2*a3*x*f(x) + a1*a2*x^2*diff(f(x), x) + a1*a3*x^2*diff(f(x), x) + a2*a3*x^2*diff(f(x), x)

and I would like to rewrite that part as

    a1*a2*a3*x*f(x) + (a1*a2*x^2*+ a1*a3*x^2+ a2*a3*x^2)*diff(f(x), x)

How do I tell Sage to do this?

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answered 2017-07-10 19:25:14 +0200

calc314 gravatar image

Try this:

p=a1*a2*a3*x*f(x) + a1*a2*x^2*diff(f(x), x) + a1*a3*x^2*diff(f(x), x) + a2*a3*x^2*diff(f(x), x)
p.collect(diff(f(x),x))
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Note that this only collects first derivatives: to collect the second, third, etc. derivatives you'd have to do that explicitly (and know how high your derivatives go).

Ursula gravatar imageUrsula ( 2017-07-18 14:55:53 +0200 )edit

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Asked: 2017-07-10 16:41:23 +0200

Seen: 182 times

Last updated: Jul 10 '17