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LREtools

ValuesAtPoint

formulas for the values of the solution of difference equation and its derivatives of the given order and at the given point.

Calling Sequence

ValuesAtPoint(L, E, fun, HalfInt_opt, Point_opt, Order_opt)

Parameters

L

-

linear difference operator in E with coefficients which are polynomials in x

E

-

name of the shift operator acting on x

fun

-

function f(x) that is a solution of Lfx=0

HalfInt_opt

-

(optional) 'HalfInterval'= A, A is a rational number, 0 by default

Point_opt

-

(optional) 'Point'=p, p is a rational number or an algebraic number in the indexed RootOf representation (see,RootOf,indexed ), 0 by default

Order_opt

-

(optional) 'OrderDer'=m, m is non-negative integer, 0 by default.

Description

The ValuesAtPoint command returns formulas for the values of the function and its derivatives of the given order and at the given point in Point_opt. It also computes conditions for the analyticity of the function at the given point.

The input includes a difference operator

>

L := Sum(a[i](x)* E^i,i=0..d);

Li=0daixEi

(1)

and the point A. Specify the point 'Point'=p to compute the value f(x) and its derivatives at x=p, and non-negative integer via the option Order_opt to specify the highest order of required derivatives of f(x) at x=p.

The procedure returns 2 sets:

1.

The set of conditions. f(x) is assumed to be analytic on some open set which contains a set A<=Rex<A+d. Elements of the set give the conditions of the analyticity of f(x) at x=p. They are relations between the values of the function and, possibly several of its derivatives at the points into A<=Rex<A+d.

2.

The set of formulas for computing fp,&DifferentialD;&DifferentialD;pfp,...,&DifferentialD;m&DifferentialD;pmfp. (f(x) must satisfy the conditions in the first set.) These formulas give the values of fp,&DifferentialD;&DifferentialD;pfp,...,&DifferentialD;m&DifferentialD;pmfp as linear combinations of f(x) and several of its derivatives in A<=Rex<A+d. For m=0, we have one unique formula for fp.

Examples

>

withLREtools&colon;

>

L1xE23x3E+2x312x+4

L1xE23x3E+2x312x+4

(2)
>

ValuesAtPointL1&comma;E&comma;fx&comma;HalfInterval=2&comma;Point=13

f113=18f835,f13=2f8375+&DifferentialD;&DifferentialD;xfxx=83|&DifferentialD;&DifferentialD;xfxx=83440+&DifferentialD;&DifferentialD;xfxx=113|&DifferentialD;&DifferentialD;xfxx=1131584

(3)
>

ValuesAtPointL1&comma;E&comma;fx&comma;HalfInterval=2&comma;Point=RootOfx2+1&comma;x&comma;index=1&comma;OrderDer=5

,&DifferentialD;5&DifferentialD;x5fxx=I|&DifferentialD;5&DifferentialD;x5fxx=I=3ID5f2+I2600048839499533961If2+I18854722656250000+556477ID3f2+I549250000+46962840717153If3+I18854722656250000+60416991ID2f2+I22313281250+549ID4f3+I3380000+357ID4f2+I338000021134484ID2f3+I11156640625+219283ID3f3+I1098500000ID5f3+I208000+68810341503IDf2+I5801453125000025780729047IDf3+I29007265625000250202038329Df2+I58014531250000+190021307517Df3+I58014531250000204172941D2f3+I357012500000368697D3f3+I549250000+577D4f3+I13520000+D5f3+I416003853718024019f2+I2356840332031250+8319818839971f3+I18854722656250000178457979D2f2+I178506250000+329139D3f2+I549250000+529D4f2+I3380000+43D5f2+I624000&comma;&DifferentialD;4&DifferentialD;x4fxx=I|&DifferentialD;4&DifferentialD;x4fxx=I=68810341503If2+I58014531250000+357ID3f2+I84500025780729047If3+I29007265625000+1669431ID2f2+I549250000ID4f3+I41600+3ID4f2+I5200+657849ID2f3+I1098500000+549ID3f3+I845000+60416991IDf2+I1115664062542268968IDf3+I11156640625178457979Df2+I89253125000204172941Df3+I1785062500001106091D2f3+I549250000+577D3f3+I3380000+D4f3+I8320250202038329f2+I58014531250000+190021307517f3+I58014531250000+987417D2f2+I549250000+529D3f2+I845000+43D4f2+I124800&comma;&DifferentialD;3&DifferentialD;x3fxx=I|&DifferentialD;3&DifferentialD;x3fxx=I=60416991If2+I11156640625+1669431IDf2+I274625000+657849IDf3+I549250000+3ID3f2+I130042268968If3+I11156640625+1071ID2f2+I845000+1647ID2f3+I845000ID3f3+I10400+987417Df2+I2746250001106091Df3+I274625000+1731D2f3+I3380000+D3f3+I2080178457979f2+I89253125000204172941f3+I178506250000+1587D2f2+I845000+43D3f2+I31200&comma;&DifferentialD;2&DifferentialD;x2fxx=I|&DifferentialD;2&DifferentialD;x2fxx=I=1071IDf2+I422500+1647IDf3+I4225003ID2f3+I10400+1669431If2+I274625000+657849If3+I549250000+9ID2f2+I1300+1587Df2+I422500+1731Df3+I1690000+3D2f3+I2080+987417f2+I2746250001106091f3+I274625000+43D2f2+I10400&comma;&DifferentialD;&DifferentialD;xfxx=I|&DifferentialD;&DifferentialD;xfxx=I=9IDf2+I6503IDf3+I5200+1071If2+I422500+1647If3+I422500+43Df2+I5200+3Df3+I1040+1587f2+I422500+1731f3+I1690000&comma;fI=9If2+I6503If3+I5200+43f2+I5200+3f3+I1040

(4)
>

ValuesAtPointL1&comma;E&comma;fx&comma;HalfInterval=0&comma;Point=2

f1=4f0,f2=40f0+12&DifferentialD;&DifferentialD;xfxx=0|&DifferentialD;&DifferentialD;xfxx=03&DifferentialD;&DifferentialD;xfxx=1|&DifferentialD;&DifferentialD;xfxx=1

(5)
>

ValuesAtPointL1&comma;E&comma;fx&comma;HalfInterval=0&comma;Point=10&comma;OrderDer=3

f1=4f0,&DifferentialD;3&DifferentialD;x3fxx=10|&DifferentialD;3&DifferentialD;x3fxx=10=2713158528557f020000+13102438497001&DifferentialD;&DifferentialD;xfxx=0|&DifferentialD;&DifferentialD;xfxx=0120000+83425799085959&DifferentialD;&DifferentialD;xfxx=1|&DifferentialD;&DifferentialD;xfxx=1480000+367470002559&DifferentialD;2&DifferentialD;x2fxx=1|&DifferentialD;2&DifferentialD;x2fxx=18000+355444180401&DifferentialD;2&DifferentialD;x2fxx=0|&DifferentialD;2&DifferentialD;x2fxx=02000+12791427403&DifferentialD;3&DifferentialD;x3fxx=0|&DifferentialD;3&DifferentialD;x3fxx=01503257675041&DifferentialD;3&DifferentialD;x3fxx=1|&DifferentialD;3&DifferentialD;x3fxx=1200+58109611&DifferentialD;4&DifferentialD;x4fxx=0|&DifferentialD;4&DifferentialD;x4fxx=01058109611&DifferentialD;4&DifferentialD;x4fxx=1|&DifferentialD;4&DifferentialD;x4fxx=140&comma;&DifferentialD;2&DifferentialD;x2fxx=10|&DifferentialD;2&DifferentialD;x2fxx=10=402200989929f0500+367470002559&DifferentialD;&DifferentialD;xfxx=1|&DifferentialD;&DifferentialD;xfxx=14000+355444180401&DifferentialD;&DifferentialD;xfxx=0|&DifferentialD;&DifferentialD;xfxx=01000+12791427403&DifferentialD;2&DifferentialD;x2fxx=0|&DifferentialD;2&DifferentialD;x2fxx=0509773025123&DifferentialD;2&DifferentialD;x2fxx=1|&DifferentialD;2&DifferentialD;x2fxx=1200+116219222&DifferentialD;3&DifferentialD;x3fxx=0|&DifferentialD;3&DifferentialD;x3fxx=0558109611&DifferentialD;3&DifferentialD;x3fxx=1|&DifferentialD;3&DifferentialD;x3fxx=110&comma;&DifferentialD;&DifferentialD;xfxx=10|&DifferentialD;&DifferentialD;xfxx=10=18072854574f025+12791427403&DifferentialD;&DifferentialD;xfxx=0|&DifferentialD;&DifferentialD;xfxx=0259773025123&DifferentialD;&DifferentialD;xfxx=1|&DifferentialD;&DifferentialD;xfxx=1100+348657666&DifferentialD;2&DifferentialD;x2fxx=0|&DifferentialD;2&DifferentialD;x2fxx=05174328833&DifferentialD;2&DifferentialD;x2fxx=1|&DifferentialD;2&DifferentialD;x2fxx=110&comma;f10=603680456f05+697315332&DifferentialD;&DifferentialD;xfxx=0|&DifferentialD;&DifferentialD;xfxx=05174328833&DifferentialD;&DifferentialD;xfxx=1|&DifferentialD;&DifferentialD;xfxx=15

(6)

References

Abramov, S.A., and van Hoeij, M. "Set of Poles of Solutions of Linear Difference Equations with Polynomial Coefficients." Computation Mathematics and Mathematical Physics. Vol. 43 No. 1. (2003): 57-62.


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