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MultivariatePowerSeries

 GetRays
 get the rays used to generate a Puiseux series

 Calling Sequence GetRays(s)

Parameters

 s - Puiseux series generated by this package

Description

 • This command returns the rays generating the cone containing the support of a Puiseux series s.
 • A Puiseux series is a power series in rational powers of the variables. More precisely:
 – Let $X≔\left({x}_{1},\dots ,{x}_{p}\right)$ and $U≔\left({u}_{1},\dots ,{u}_{m}\right)$ be ordered lists of variables.
 – Let $R≔\left({r}_{1},\dots ,{r}_{m}\right)$ be a list of $m$ grevlex-positive $p$-dimensional rational vectors.
 – Let $e≔\left({e}_{1},\dots ,{e}_{p}\right)$ be a point in ${\mathrm{ℚ}}^{p}$.
 – Let $g\left(U\right)≔{\sum }_{n=0}^{\mathrm{\infty }}{g}_{n}\left(U\right)$ be a multivariate power series in $U$ with homogeneous components ${g}_{n}\left(U\right)$.
 For any $v=\left({v}_{1},\dots ,{v}_{q}\right)$ in ${\mathrm{ℚ}}^{q}$ and any list $Y=\left({y}_{1},\dots ,{y}_{q}\right)$, we write ${Y}^{v}$ for ${y}_{1}^{{v}_{1}}\dots {y}_{q}^{{v}_{q}}$. Moreover, we write ${X}^{R}$ for the list $\left({X}^{{r}_{1}},\dots ,{X}^{{r}_{m}}\right)$ of $m$ products of powers of the variables in $X$. Then $P≔{X}^{e}g\left({X}^{R}\right)$ is a Puiseux series, and every Puiseux series can be written in this way. This can be understood as evaluating $g\left(U\right)$ at ${u}_{i}={X}^{{r}_{i}}$ and then multiplying the result by ${X}^{e}$.
 • We call $g$ the internal power series of the Puiseux series $P$; $X$ the variable order of $P$; $U$ the variable order of $g$; and $R$ the rays of $P$. The rays generate the cone containing the support of $P$, meaning the set of exponent vectors of $X$ that occur in $P$ with a nonzero coefficient, as in the paper by Monforte and Kauers (see References). The vertex of this cone is $e$.
 • When using the MultivariatePowerSeries package, do not assign anything to the variables occurring in the power series, Puiseux series, and univariate polynomials over these series. If you do, you may see invalid results.

Examples

 > $\mathrm{with}\left(\mathrm{MultivariatePowerSeries}\right):$

Create two Puiseux series.

 > $p≔\mathrm{PowerSeries}\left(1+uv\right);$$X≔\left[x,y\right];$$U≔\left[u,v\right];$$R≔\left[\left[1,0\right],\left[1,-1\right]\right];$$E≔\left[x=-5,y=3\right]$
 ${p}{≔}\left[{PowⅇrSⅇriⅇs:}{1}{+}{u}{}{v}\right]$
 ${X}{≔}\left[{x}{,}{y}\right]$
 ${U}{≔}\left[{u}{,}{v}\right]$
 ${R}{≔}\left[\left[{1}{,}{0}\right]{,}\left[{1}{,}{-1}\right]\right]$
 ${E}{≔}\left[{x}{=}{-5}{,}{y}{=}{3}\right]$ (1)
 > $\mathrm{s1}≔\mathrm{PuiseuxSeries}\left(p,X,U,R,E\right)$
 ${\mathrm{s1}}{≔}\left[{PuisⅇuxSⅇriⅇs of}\frac{\left(\frac{{{x}}^{{2}}}{{y}}{+}{1}\right){}{{y}}^{{3}}}{{{x}}^{{5}}}{:}\frac{{{y}}^{{3}}}{{{x}}^{{5}}}{+}\frac{{{y}}^{{2}}}{{{x}}^{{3}}}\right]$ (2)
 > $\mathrm{s2}≔\mathrm{PuiseuxSeries}\left(\frac{1}{1+uv},\left[u=x{y}^{0},v=x{y}^{-1}\right],\left[x=5,y=-3\right]\right)$
 ${\mathrm{s2}}{≔}\left[{PuisⅇuxSⅇriⅇs of}\frac{{{x}}^{{5}}}{\left(\frac{{{x}}^{{2}}}{{y}}{+}{1}\right){}{{y}}^{{3}}}{:}\frac{{{x}}^{{5}}}{{{y}}^{{3}}}{+}{\dots }\right]$ (3)

We get the rays of s1.

 > $\mathrm{GetRays}\left(\mathrm{s1}\right)$
 $\left[\left[{1}{,}{0}\right]{,}\left[{1}{,}{-1}\right]\right]$ (4)

We get the rays of s2.

 > $\mathrm{GetRays}\left(\mathrm{s2}\right)$
 $\left[\left[{1}{,}{0}\right]{,}\left[{1}{,}{-1}\right]\right]$ (5)

References

 Monforte, A.A., & Kauers, M. "Formal Laurent series in several variables." Expositiones Mathematicae. Vol. 31 No. 4 (2013): 350-367.

Compatibility

 • The MultivariatePowerSeries[GetRays] command was introduced in Maple 2023.
 • For more information on Maple 2023 changes, see Updates in Maple 2023.