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Working with complex symbolic expressions

asked 2012-02-13 15:07:47 +0100

russ_hensel gravatar image

I am a beginner at Sage so my questions may not be well informed, so bear with me.

The context: I am trying to use sage to explore the exponential function assuming all I know about it is that it is its own derivative and has the value 1 at z = 0. It is then easy to develop the Taylor series to any degree using formula like:

expp2( z ) = 1 + ( 1/ factorial( 1 ) )* z + ( 1/ factorial( 2 ) ) * ( z ^ 2 )

You can take 2 of these for z = a and z = b and multiply them together in Sage. Getting something like:

1/4(b^2 + 2b + 2)(a^2 + 2a + 2)

Now I have done the algebra by hand and know this reduces to the Taylor expansion for z = a + b.

What I do not get is how to show this part in Sage in a nice clean way ( I have some ways I do not like so much ).

Here I have 2 questions one specific, and one general ( I am interested in the answer to either one or both):

1) If this exponential question interests anyone, could you offer some tips? I have tried various ( but not all ) applications of expand and simplify. I am still plugging away.

2) Is there a guide that would help me learn how to carry out algebraic operations over complex expressions. I have looked at several basic tutorials, but they do not have much detail. The most useful single resource I have found is

and the pages linking from it.

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answered 2014-07-01 17:51:21 +0100

rws gravatar image

updated 2014-07-01 17:52:30 +0100

It is quite possible to get what you want with formal power series:

sage: R.<a,b> = PowerSeriesRing(QQ); R
Multivariate Power Series Ring in a, b over Rational Field
sage: exp(a+b)==exp(a)*exp(b)
sage: exp(a-b)==exp(a)/exp(b)


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Asked: 2012-02-13 15:07:47 +0100

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Last updated: Jul 01 '14