symbolic expantion in matlab

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dav
dav 2013-3-7
hi,
I need to expand [1- (a1+b1)B ] / (1-b1B) and get a polynomial.
Can someone help me with this please?
Thanks.

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Walter Roberson
Walter Roberson 2013-3-8
A polynomial in which variable? A finite polynomial or an infinite one?
If you need an infinite polynomial in B, then the expression is, using MuPAD notation,
1-a1*(sum(B^n*b1^(n-1), n = 1 .. infinity))
There is no finite version unless you want an approximation.
The above was deduced by examining the taylor expansion around B=0
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Walter Roberson
Walter Roberson 2013-3-8
What are you expecting the polynomial might look like? And which variable should it be in? Are you looking for an exact polynomial or an approximation? If an approximation, then how close does it need to be? Are there constraints on the values of a1, b1, or B ?
dav
dav 2013-3-8
I need a polynomial with at least 20 terms. I am actually tying to print a few terms of the infinite ar representation of the arma model in time series.
Also its better if I could have a constraint that a,b>0 and a+b<1 in it.
Finally i would like the code to print something like
1 - a1*B - a1*B^2*b1 - a1*B^3*b1^2 - a1*B^4*b1^3 ....
Again, Tanks a lot for all the help!

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