Expand , Degree , Coef , Content , PrimitivePart , LeadingCoef , Monic , RandomPoly , Horner , ExpandBrackets , OrthoP , OrthoH , OrthoG , OrthoL , OrthoT, OrthoU , OrthoPSum, OrthoHSum, OrthoLSum, OrthoGSum, OrthoTSum, OrthoUSum , OrthoPoly , OrthoPolySum .

# Polynomials

This chapter contains commands to manipulate polynomials. This includes functions for constructing and evaluating orthogonal polynomials.

Expand | put polynomial in expanded form
Degree | degree of a polynomial
Coef | coefficient of a polynomial
Content | content of a univariate polynomial
PrimitivePart | primitive part of a univariate polynomial
LeadingCoef | leading coefficient of a polynomial
Monic | monic part of a polynomial
RandomPoly | construct a random polynomial
Horner | convert polynomial into Horner form
ExpandBrackets | expand all brackets
OrthoP | Legendre and Jacobi orthogonal polynomials
OrthoH | Hermite orthogonal polynomials
OrthoG | Gegenbauer orthogonal polynomials
OrthoL | Laguerre orthogonal polynomials
OrthoT, OrthoU | Tschebyscheff polynomials
OrthoPSum, OrthoHSum, OrthoLSum, OrthoGSum, OrthoTSum, OrthoUSum | sums of series of orthogonal polynomials
OrthoPoly | internal function for constructing orthogonal polynomials
OrthoPolySum | internal function for computing series of orthogonal polynomials

###

Expand -- put polynomial in expanded form

##### Standard library

##### Calling format:

    Expand(expr)
    Expand(expr, var)
    Expand(expr, varlist)

##### Parameters:

expr - a polynomial expression

var - a variable

varlist - a list of variables

##### Description:

This command brings a polynomial in expanded form, in which polynomials are represented in the form c0+c1*x+c2*x^2+...+c[n]*x^n. In this form, it is easier to test whether a polynomial is zero, namely by testing whether all coefficients are zero.

If the polynomial "expr" contains only one variable, the first calling sequence can be used. Otherwise, the second form should be used which explicitly mentions that "expr" should be considered as a polynomial in the variable "var". The third calling form can be used for multivariate polynomials. Firstly, the polynomial "expr" is expanded with respect to the first variable in "varlist". Then the coefficients are all expanded with respect to the second variable, and so on.

##### Examples:

    In> PrettyPrinter("PrettyForm");

    True

    In> Expand((1+x)^5);

     5        4         3         2
    x  + 5 * x  + 10 * x  + 10 * x  + 5 * x + 1

    In> Expand((1+x-y)^2, x);

     2                                2
    x  + 2 * ( 1 - y ) * x + ( 1 - y )

    In> Expand((1+x-y)^2, {x,y});

     2                         2
    x  + ( -2 * y + 2 ) * x + y  - 2 * y + 1

##### See also:

ExpandBrackets .

###

Degree -- degree of a polynomial

##### Standard library

##### Calling format:

    Degree(expr)
    Degree(expr, var)

##### Parameters:

expr - a polynomial

var - a variable occurring in "expr"

##### Description:

This command returns the degree of the polynomial "expr" with respect to the variable "var". The degree is the highest power of "var" occurring in the polynomial. If only one variable occurs in "expr", the first calling sequence can be used. Otherwise the user should use the second form in which the variable is explicitly mentioned.

##### Examples:

    In> Degree(x^5+x-1);
    Out> 5;
    In> Degree(a+b*x^3, a);
    Out> 1;
    In> Degree(a+b*x^3, x);
    Out> 3;

##### See also:

Expand , Coef .

###

Coef -- coefficient of a polynomial

##### Standard library

##### Calling format:

    Coef(expr, var, order)

##### Parameters:

expr - a polynomial

var - a variable occurring in "expr"

order - integer or list of integers

##### Description:

This command returns the coefficient of "var" to the power "order" in the polynomial "expr". The parameter "order" can also be a list of integers, in which case this function returns a list of coefficients.

##### Examples:

    In> e := Expand((a+x)^4,x)
    Out> x^4+4*a*x^3+(a^2+(2*a)^2+a^2)*x^2+
    (a^2*2*a+2*a^3)*x+a^4;
    In> Coef(e,a,2)
    Out> 6*x^2;
    In> Coef(e,a,0 .. 4)
    Out> {x^4,4*x^3,6*x^2,4*x,1};

##### See also:

Expand , Degree , LeadingCoef .

###

Content -- content of a univariate polynomial

##### Standard library

##### Calling format:

    Content(expr)

##### Parameters:

expr - univariate polynomial

##### Description:

This command determines the content of a univariate polynomial. The content is the greatest common divisor of all the terms in the polynomial. Every polynomial can be written as the product of the content with the primitive part.

##### Examples:

    In> poly := 2*x^2 + 4*x;
    Out> 2*x^2+4*x;
    In> c := Content(poly);
    Out> 2*x;
    In> pp := PrimitivePart(poly);
    Out> x+2;
    In> Expand(pp*c);
    Out> 2*x^2+4*x;

##### See also:

PrimitivePart , Gcd .

###

PrimitivePart -- primitive part of a univariate polynomial

##### Standard library

##### Calling format:

    PrimitivePart(expr)

##### Parameters:

expr - univariate polynomial

##### Description:

This command determines the primitive part of a univariate polynomial. The primitive part is what remains after the content (the greatest common divisor of all the terms) is divided out. So the product of the content and the primitive part equals the original polynomial.

##### Examples:

    In> poly := 2*x^2 + 4*x;
    Out> 2*x^2+4*x;
    In> c := Content(poly);
    Out> 2*x;
    In> pp := PrimitivePart(poly);
    Out> x+2;
    In> Expand(pp*c);
    Out> 2*x^2+4*x;

##### See also:

Content .

###

LeadingCoef -- leading coefficient of a polynomial

##### Standard library

##### Calling format:

    LeadingCoef(poly)
    LeadingCoef(poly, var)

##### Parameters:

poly - a polynomial

var - a variable

##### Description:

This function returns the leading coefficient of "poly", regarded as a polynomial in the variable "var". The leading coefficient is the coefficient of the term of highest degree. If only one variable appears in the expression "poly", it is obvious that it should be regarded as a polynomial in this variable and the first calling sequence may be used.

##### Examples:

    In> poly := 2*x^2 + 4*x;
    Out> 2*x^2+4*x;
    In> lc := LeadingCoef(poly);
    Out> 2;
    In> m := Monic(poly);
    Out> x^2+2*x;
    In> Expand(lc*m);
    Out> 2*x^2+4*x;

    In> LeadingCoef(2*a^2 + 3*a*b^2 + 5, a);
    Out> 2;
    In> LeadingCoef(2*a^2 + 3*a*b^2 + 5, b);
    Out> 3*a;

##### See also:

Coef , Monic .

###

Monic -- monic part of a polynomial

##### Standard library

##### Calling format:

    Monic(poly)
    Monic(poly, var)

##### Parameters:

poly - a polynomial

var - a variable

##### Description:

This function returns the monic part of "poly", regarded as a polynomial in the variable "var". The monic part of a polynomial is the quotient of this polynomial by its leading coefficient. So the leading coefficient of the monic part is always one. If only one variable appears in the expression "poly", it is obvious that it should be regarded as a polynomial in this variable and the first calling sequence may be used.

##### Examples:

    In> poly := 2*x^2 + 4*x;
    Out> 2*x^2+4*x;
    In> lc := LeadingCoef(poly);
    Out> 2;
    In> m := Monic(poly);
    Out> x^2+2*x;
    In> Expand(lc*m);
    Out> 2*x^2+4*x;

    In> Monic(2*a^2 + 3*a*b^2 + 5, a);
    Out> a^2+(a*3*b^2)/2+5/2;
    In> Monic(2*a^2 + 3*a*b^2 + 5, b);
    Out> b^2+(2*a^2+5)/(3*a);

##### See also:

LeadingCoef .

###

RandomPoly -- construct a random polynomial

##### Standard library

##### Calling format:

    RandomPoly(var,deg,coefmin,coefmax)

##### Parameters:

var - free variable for resulting univariate polynomial

deg - degree of resulting univariate polynomial

coefmin - minimum value for coefficients

coefmax - maximum value for coefficients

##### Description:

RandomPoly generates a random polynomial in variable "var", of degree "deg", with integer coefficients ranging from "coefmin" to "coefmax" (inclusive). The coefficients are uniformly distributed in this interval, and are independent of each other.

##### Examples:

    In> RandomPoly(x,3,-10,10)
    Out> 3*x^3+10*x^2-4*x-6;
    In> RandomPoly(x,3,-10,10)
    Out> -2*x^3-8*x^2+8;

##### See also:

Random , RandomIntegerVector .

###

Div and Mod for polynomials

##### Standard library

Div and Mod are also defined for polynomials.

##### See also:

Div , Mod .

###

Horner -- convert polynomial into Horner form

##### Standard library

##### Calling format:

    Horner(expr, var)

##### Parameters:

expr - a polynomial in "var"

var - a variable

##### Description:

This command turns the polynomial "expr", considered as a univariate polynomial in "var", into Horner form. A polynomial in normal form is an expression such as

c[0]+c[1]*x+...+c[n]*x^n.

If one converts this polynomial into Horner form, one gets the equivalent expression

(...(c[n]*x+c[n-1])*x+...+c[1])*x+c[0].

Both expression are equal, but the latter form gives a more efficient way to evaluate the polynomial as the powers have disappeared.

##### Examples:

    In> expr1:=Expand((1+x)^4)
    Out> x^4+4*x^3+6*x^2+4*x+1;
    In> Horner(expr1,x)
    Out> (((x+4)*x+6)*x+4)*x+1;

##### See also:

Expand , ExpandBrackets .

###

ExpandBrackets -- expand all brackets

##### Standard library

##### Calling format:

    ExpandBrackets(expr)

##### Parameters:

expr - an expression

##### Description:

This command tries to expand all the brackets by repeatedly using the distributive laws a*(b+c)=a*b+a*c and (a+b)*c=a*c+b*c. It goes further than `Expand`, in that it expands all terms.

##### Examples:

    In> Expand((a-x)*(b-x),x)
    Out> x^2-(b+a)*x+a*b;
    In> Expand((a-x)*(b-x),{x,a,b})
    Out> x^2-(b+a)*x+b*a;
    In> ExpandBrackets((a-x)*(b-x))
    Out> a*b-x*b+x^2-a*x;

##### See also:

Expand .

###

OrthoP -- Legendre and Jacobi orthogonal polynomials

##### Standard library

##### Calling format:

    OrthoP(n, x);
    OrthoP(n, a, b, x);

##### Parameters:

n - degree of polynomial

x - point to evaluate polynomial at

a, b - parameters for Jacobi polynomial

##### Description:

The first calling format with two arguments evaluates the Legendre polynomial of degree "n" at the point "x". The second form does the same for the Jacobi polynomial with parameters "a" and "b", which should be greater than -1.

The Jacobi polynomials are orthogonal with respect to the weight function (1-x)^a*(1+x)^b on the interval [-1,1]. They satisfy the recurrence relations:

    P(0,a,b,x) = 1

                 a - b     /     a + b \
    P(1,a,b,x) = ----- + x | 1 + ----- |
                   2       \       2   /

    P(n,a,b,x) = (2n + a + b - 1) *

        2   2
       a - b + x (2n+a+b-2) (n+a+b)
       ---------------------------- P(n-1,a,b,x)
          2n (2n+a+b-2) (n+a+b)

        (n+a-1) (n+b-1) (2n+a+b)
     -  ------------------------ P(n-2,a,b,x),
          n (n+a+b) (2n+a+b-2)

for n>1.

Legendre polynomials are a special case of Jacobi polynomials with the specific parameter values a = b = 0. So they form an orthogonal system with respect to the weight function identically equal to 1 on the interval [-1,1], and they satisfy the recurrence relations:

    P(0,x) = 1

    P(1,x) = x

             (2n - 1) x            n - 1
    P(n,x) = ---------- P(n-1,x) - ----- P(n-2,x),
                 2n                  n

for n>1.

Most of the work is performed by the internal function `OrthoPoly`.

##### Examples:

    In> PrettyPrinter("PrettyForm");

    True

    In> OrthoP(3, x);

        /      2     \
        | 5 * x    3 |
    x * | ------ - - |
        \   2      2 /

    In> OrthoP(3, 1, 2, x);

    1       /     / 21 * x   7 \   7 \
    - + x * | x * | ------ - - | - - |
    2       \     \   2      2 /   2 /

    In> Expand(%)

          3        2
    21 * x  - 7 * x  - 7 * x + 1
    ----------------------------
                 2

    In> OrthoP(3, 1, 2, 0.5);

    -0.8124999999

##### See also:

OrthoPSum , OrthoG , OrthoPoly .

###

OrthoH -- Hermite orthogonal polynomials

##### Standard library

##### Calling format:

    OrthoH(n, x);

##### Parameters:

n - degree of polynomial

x - point to evaluate polynomial at

##### Description:

This function evaluates the Hermite polynomial of degree "n" at the point "x".

The Hermite polynomials are orthogonal with respect to the weight function Exp(-x^2/2) on the entire real axis. They satisfy the recurrence relations:

    H(0,x) = 1

    H(1,x) = 2x

    H(n,x) = 2x H(n-1,x) - 2(n-1) H(n-2,x),

for n>1.

Most of the work is performed by the internal function `OrthoPoly`.

##### Examples:

    In> OrthoH(3, x);
    Out> x*(8*x^2-12);
    In> OrthoH(6, 0.5);
    Out> 31;

##### See also:

OrthoHSum , OrthoPoly .

###

OrthoG -- Gegenbauer orthogonal polynomials

##### Standard library

##### Calling format:

    OrthoG(n, a, x);

##### Parameters:

n - degree of polynomial

a - parameter

x - point to evaluate polynomial at

##### Description:

This function evaluates the Gegenbauer (or ultraspherical) polynomial with parameter "a" and degree "n" at the point "x". The parameter "a" should be greater than -1/2.

The Gegenbauer polynomials are orthogonal with respect to the weight function (1-x^2)^(a-1/2) on the interval [-1,1]. Hence they are connected to the Jacobi polynomials via G(n, a, x) = P(n, a-1/2, a-1/2, x). They satisfy the recurrence relations:

    G(0,a,x) = 1

    G(1,a,x) = 2 x

                 /     a - 1 \
    G(n,a,x) = 2 | 1 + ----- | x G(n-1,a,x)
                 \       n   /

      /     2 (a-2) \
    - | 1 + ------- | G(n-2,a,x),
      \        n    /

for n>1.

Most of the work is performed by the internal function `OrthoPoly`.

##### Examples:

    In> OrthoG(5, 1, x);
    Out> x*((32*x^2-32)*x^2+6);
    In> OrthoG(5, 2, -0.5);
    Out> 2;

##### See also:

OrthoP , OrthoT , OrthoU , OrthoGSum , OrthoPoly .

###

OrthoL -- Laguerre orthogonal polynomials

##### Standard library

##### Calling format:

    OrthoL(n, a, x);

##### Parameters:

n - degree of polynomial

a - parameter

x - point to evaluate polynomial at

##### Description:

This function evaluates the Laguerre polynomial with parameter "a" and degree "n" at the point "x". The parameter "a" should be greater than -1.

The Laguerre polynomials are orthogonal with respect to the weight function x^a*Exp(-x) on the positive real axis. They satisfy the recurrence relations:

    L(0,a,x) = 1

    L(1,a,x) = a + 1 - x

               /     a - 1 - x \
    L(n,a,x) = | 2 + --------- | L(n-1,a,x) -
               \         n     /

      /     a - 1 \
      | 1 + ----- | L(n-2,a,x),
      \  	  n   /

for n>1.

Most of the work is performed by the internal function `OrthoPoly`.

##### Examples:

    In> OrthoL(3, 1, x);
    Out> x*(x*(2-x/6)-6)+4;
    In> OrthoL(3, 1/2, 0.25);
    Out> 1.2005208334;

##### See also:

OrthoLSum , OrthoPoly .

###

OrthoT, OrthoU -- Tschebyscheff polynomials

##### Standard library

##### Calling format:

    OrthoT(n, x);
    OrthoU(n, x);

##### Parameters:

n - degree of polynomial

x - point to evaluate polynomial at

##### Description:

These functions evaluate the Tschebyscheff polynomials of the first kind T(n,x) and of the second kind U(n,x), of degree "n" at the point "x". (The name of this Russian mathematician is also sometimes spelled "Chebyshev".)

The Tschebyscheff polynomials are orthogonal with respect to the weight function (1-x^2)^(-1/2). Hence they are a special case of the Gegenbauer polynomials G(n,a,x), with a=0. They satisfy the recurrence relations:

    T(n,x) = 2 x T(n-1,x) - T(n-2,x),
    U(n,x) = 2 x U(n-1,x) - U(n-2,x)

for n>1, with

    T(0,x) = 1,
    T(1,x) = x,
    U(0,x) = 1,
    U(1,x) = 2 x.

Tschebyscheff polynomials are evaluated using fast (but numerically unstable) recurrence relations,

T(2*n,x)=2*T(n,x)^2-1,

T(2*n+1,x)=2*T(n+1,x)*T(n,x)-x,

U(2*n,x)=2*T(n,x)*U(n,x)-1,

U(2*n+1,x)=2*T(n+1,x)*U(n,x).
This allows to compute T(n,x) and U(n,x) in time logarithmic in n. Note that the functions return the polynomials in a sparse unexpanded form.

Warning: because of numerical instability of this algorithm, polynomials of very large orders on floating-point arguments should be evaluated with increased precision.

##### Examples:

    In> OrthoT(3, x);
    Out> 2*x*(2*x^2-1)-x;
    In> OrthoT(10, 0.9);
    Out> -0.2007474688;
    In> OrthoU(3, x);
    Out> 4*x*(2*x^2-1);
    In> OrthoU(10, 0.9);
    Out> -2.2234571776;

Here is an example numerical calculation where the loss of precision is catastrophic:

    In> OrthoT(10000000000001, 0.9)
    Out> 0.1851470834;
    In> Precision(20);
    Out> True;
    In> OrthoT(10000000000001, 0.9)
    Out> -0.79727552022438356731;

##### See also:

OrthoG , OrthoTSum , OrthoUSum , OrthoPoly .

###

OrthoPSum, OrthoHSum, OrthoLSum, OrthoGSum, OrthoTSum, OrthoUSum -- sums of series of orthogonal polynomials

##### Standard library

##### Calling format:

    OrthoPSum(c, x);
    OrthoPSum(c, a, b, x);
    OrthoHSum(c, x);
    OrthoLSum(c, a, x);
    OrthoGSum(c, a, x);
    OrthoTSum(c, x);
    OrthoUSum(c, x);

##### Parameters:

c - list of coefficients

a, b - parameters of specific polynomials

x - point to evaluate polynomial at

##### Description:

These functions evaluate the sum of series of orthogonal polynomials at the point "x", with given list of coefficients "c" of the series and fixed polynomial parameters "a", "b" (if applicable).

The list of coefficients starts with the lowest order, so that for example OrthoLSum(c, a, x) = c[1]* L[0](a,x) + c[2] L[1](a,x) + ... + c[N] L[N-1](a,x).

See pages for specific orthogonal polynomials for more details on the parameters of the polynomials.

Most of the work is performed by the internal function `OrthoPolySum`. The individual polynomials entering the series are not computed, only the sum of the series.

##### Examples:

    In> Expand(OrthoPSum({1,0,0,1/7,1/8}, 3/2, \
      2/3, x));
    Out> (7068985*x^4)/3981312+(1648577*x^3)/995328+
    (-3502049*x^2)/4644864+(-4372969*x)/6967296
    +28292143/27869184;

##### See also:

OrthoP , OrthoG , OrthoH , OrthoL , OrthoT , OrthoU , OrthoPolySum .

###

OrthoPoly -- internal function for constructing orthogonal polynomials

##### Standard library

##### Calling format:

    OrthoPoly(name, n, par, x)

##### Parameters:

name - string containing name of orthogonal family

n - degree of the polynomial

par - list of values for the parameters

x - point to evaluate at

##### Description:

This function is used internally to construct orthogonal polynomials. It returns the "n"-th polynomial from the family "name" with parameters "par" at the point "x".

All known families are stored in the association list `KnownOrthoPoly`. The name serves as key. At the moment the following names are known to Yacas: `"Jacobi"`, `"Gegenbauer"`, `"Laguerre"`, `"Hermite"`, `"Tscheb1"`, and `"Tscheb2"`. The value associated to the key is a pure function that takes two arguments: the order `n` and the extra parameters `p`, and returns a list of two lists: the first list contains the coefficients `A,B` of the n=1 polynomial, i.e. A+B*x; the second list contains the coefficients `A,B,C` in the recurrence relation, i.e. P[n]=(A+B*x)*P[n-1]+C*P[n-2]. (There are only 3 coefficients in the second list, because none of the polynomials use C+D*x instead of C in the recurrence relation. This is assumed in the implementation!)

If the argument `x` is numerical, the function `OrthoPolyNumeric` is called. Otherwise, the function `OrthoPolyCoeffs` computes a list of coefficients, and `EvaluateHornerScheme` converts this list into a polynomial expression.

##### See also:

OrthoP , OrthoG , OrthoH , OrthoL , OrthoT , OrthoU , OrthoPolySum .

###

OrthoPolySum -- internal function for computing series of orthogonal polynomials

##### Standard library

##### Calling format:

    OrthoPolySum(name, c, par, x)

##### Parameters:

`name` -- string containing name of orthogonal family

`c` -- list of coefficients

`par` -- list of values for the parameters

`x` -- point to evaluate at

##### Description:

This function is used internally to compute series of orthogonal polynomials. It is similar to the function `OrthoPoly` and returns the result of the summation of series of polynomials from the family `name` with parameters `par` at the point `x`, where `c` is the list of coefficients of the series.

The algorithm used to compute the series without first computing the individual polynomials is the Clenshaw-Smith recurrence scheme. See: Yudell L. Luke. Mathematical functions and their approximations. Academic Press, N. Y., 1975.

If the argument `x` is numerical, the function `OrthoPolySumNumeric` is called. Otherwise, the function `OrthoPolySumCoeffs` computes the list of coefficients of the resulting polynomial, and `EvaluateHornerScheme` converts this list into a polynomial expression.

##### See also:

OrthoPSum , OrthoGSum , OrthoHSum , OrthoLSum , OrthoTSum , OrthoUSum , OrthoPoly .