The FPseries and FTseries commands return a power series solution of the given linear ordinary differential equation with polynomial coefficients which must be homogeneous or inhomogeneous with a right hand side that is a polynomial, a rational function, or a "nice" power series (see LODEstruct) in the independent variable .

If ode is an expression, then it is equated to zero.

The routine returns an error message if the differential equation ode does not satisfy the following conditions.

ode must be linear in var

ode must have polynomial coefficients in

ode must be homogeneous or have a right-hand side that is rational or a "nice" power series in

The coefficients of ode must be either rational numbers or depend rationally on one or more parameters.

A homogeneous linear ordinary differential equation with coefficients that are polynomials in  has a linear space of formal power series solutions  where  is one of , , , or ,  is the expansion point, and the sequence  satisfies a homogeneous linear recurrence. In the case of an inhomogeneous equation with a right-hand side that is a "nice" power series,  satisfies an inhomogeneous linear recurrence.

The routines choose a polynomial basis depending on the expansion point. If  is a rational or algebraic number, then the basis is  for FPseries and  for FTseries. If , then the basis is  for FPseries and  for FTseries.

Both routines then build a linear recurrence  for the sequence of coefficients of the series solution in the chosen basis. They determine the number  of initial values of this sequence so that it is possible to calculate any element from these initial values using the recurrence (taking into account the order and the zeros of the leading coefficients of the recurrence), and calculate these initial values.

The formal power series is represented by an FPSstruct data structure:

where  are expressions, the initial series coefficients.

In the case of an inhomogeneous equation with a rational right hand side the commands work similarly. In the case of a "nice" power series right hand side the recurrence  is inhomogeneous.

x=a or 'point'=a

Specifies the expansion point in the case of a homogeneous equation or an inhomogeneous equation with rational right-hand side. The default is . It can be an algebraic number, depending rationally on some parameters, or . In the case of a "nice" series right-hand side the expansion point is given by the right-hand side and cannot be changed.

'terms'=N

Specifies a nonnegative integer N, the required number of initial terms of the series solutions. If this option is given, then the routine compares it with the determined number  and, if , calculates the first N initial coefficients.

'free'=C

Specifies a base name C to use for free variables C[0], C[1], etc. The default is the global name  _C. Note that the number of free variables may be less than the order of the given equation if the expansion point is singular.