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From: Nick Todd on 23 May 2010 21:50
Walter Roberson <roberson(a)hushmail.com> wrote in message <8TbKn.30272$wV2.27818(a)newsfe23.iad>...
> Nick Todd wrote:
> > I need to be able to represent a symbolic expression such as y = a^5*X^3
> > + X + 1 , where the X^2 term is not present, as a vector ie. [a^5 0 1 1]
> >
> > I cannot use sym2poly because the expression contains more than one
> > symbolic variable. The coeffs function seems appropriate but doesn't
> > include the zero coefficient of X^2 ie returns [a^5, 1, 1].
> >
> > How can I get a coefficient vector which contains any zero coefficients
> > that might be present in the symbolic representation?
>
> See
> http://www.mathworks.com/matlabcentral/newsreader/view_thread/276491#730341
> "Extract numbers (coefficients) from a polynomial (sym)"

Thanks Walter, do you know how i can do this using matlab code only?

I'm thinking i could build the vector manually from the two output version of coeffs but i need to know the power attached to each X term present. Is there a function to find the degree of a symbolic expression?
From: Walter Roberson on 23 May 2010 22:34
Nick Todd wrote:
> Walter Roberson <roberson(a)hushmail.com> wrote in message
> <8TbKn.30272$wV2.27818(a)newsfe23.iad>...
>> Nick Todd wrote:
>> > I need to be able to represent a symbolic expression such as y =
>> a^5*X^3 > + X + 1 , where the X^2 term is not present, as a vector ie.
>> [a^5 0 1 1]

>> See
>> http://www.mathworks.com/matlabcentral/newsreader/view_thread/276491#730341

> do you know how i can do this using matlab code only?

I think you will have to use some MuPad. Matlab itself does not provide
tools to analyze symbolic expressions.

> I'm thinking i could build the vector manually from the two output
> version of coeffs but i need to know the power attached to each X term
> present. Is there a function to find the degree of a symbolic expression?

degree()
http://www.mathworks.com/access/helpdesk/help/toolbox/mupad/stdlib/degree.html

You may wish to consider just filling in the holes after using poly2list()
http://www.mathworks.com/access/helpdesk/help/toolbox/mupad/stdlib/poly2list.html
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