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# Polynomials

## Introduction to Polynomials

Polynomials are stored in maxima either in General Form or as Cannonical Rational Expressions (CRE) form. The latter is a standard form, and is used internally by operations such as factor, ratsimp, and so on.

Canonical Rational Expressions constitute a kind of representation which is especially suitable for expanded polynomials and rational functions (as well as for partially factored polynomials and rational functions when RATFAC[FALSE] is set to TRUE). In this CRE form an ordering of variables (from most to least main) is assumed for each expression. Polynomials are represented recursively by a list consisting of the main variable followed by a series of pairs of expressions, one for each term of the polynomial. The first member of each pair is the exponent of the main variable in that term and the second member is the coefficient of that term which could be a number or a polynomial in another variable again represented in this form. Thus the principal part of the CRE form of 3*X^2-1 is (X 2 3 0 -1) and that of 2*X*Y+X-3 is (Y 1 (X 1 2) 0 (X 1 1 0 -3)) assuming Y is the main variable, and is (X 1 (Y 1 2 0 1) 0 -3) assuming X is the main variable. "Main"-ness is usually determined by reverse alphabetical order. The "variables" of a CRE expression needn't be atomic. In fact any subexpression whose main operator is not + - * / or ^ with integer power will be considered a "variable" of the expression (in CRE form) in which it occurs. For example the CRE variables of the expression X+SIN(X+1)+2*SQRT(X)+1 are X, SQRT(X), and SIN(X+1). If the user does not specify an ordering of variables by using the RATVARS function MACSYMA will choose an alphabetic one. In general, CRE's represent rational expressions, that is, ratios of polynomials, where the numerator and denominator have no common factors, and the denominator is positive. The internal form is essentially a pair of polynomials (the numerator and denominator) preceded by the variable ordering list. If an expression to be displayed is in CRE form or if it contains any subexpressions in CRE form, the symbol /R/ will follow the line label. See the RAT function for converting an expression to CRE form. An extended CRE form is used for the representation of Taylor series. The notion of a rational expression is extended so that the exponents of the variables can be positive or negative rational numbers rather than just positive integers and the coefficients can themselves be rational expressions as described above rather than just polynomials. These are represented internally by a recursive polynomial form which is similar to and is a generalization of CRE form, but carries additional information such as the degree of truncation. As with CRE form, the symbol /T/ follows the line label of such expressions.

## Definitions for Polynomials

Variable: ALGEBRAIC
  default: [FALSE] must be set to TRUE in order for the simplification of algebraic integers to take effect.

Variable: BERLEFACT
  default: [TRUE] if FALSE then the Kronecker factoring algorithm will be used otherwise the Berlekamp algorithm, which is the default, will be used.

Function: BEZOUT (p1, p2, var)
  an alternative to the RESULTANT command. It returns a matrix. DETERMINANT of this matrix is the desired resultant.

Function: BOTHCOEF (exp, var)
  returns a list whose first member is the coefficient of var in exp (as found by RATCOEF if exp is in CRE form otherwise by COEFF) and whose second member is the remaining part of exp. That is, [A,B] where exp=A*var+B.

      (C1) ISLINEAR(EXP,VAR):=BLOCK([C],
              C:BOTHCOEF(RAT(EXP,VAR),VAR),
              IS(FREEOF(VAR,C) AND C[1]#0))$
      (C2) ISLINEAR((R**2-(X-R)**2)/X,X);
      (D2)                              TRUE

Function: COEFF (exp, v, n)
  obtains the coefficient of v**n in exp. n may be omitted if it is 1. v may be an atom, or complete subexpression of exp e.g., X, SIN(X), A[I+1], X+Y, etc. (In the last case the expression (X+Y) should occur in exp). Sometimes it may be necessary to expand or factor exp in order to make v^n explicit. This is not done automatically by COEFF.

      (C1) COEFF(2*A*TAN(X)+TAN(X)+B=5*TAN(X)+3,TAN(X));
      (D1)                         2 A + 1 = 5
      (C2) COEFF(Y+X*%E**X+1,X,0);
      (D2)                            Y + 1

Function: COMBINE (exp)
  simplifies the sum exp by combining terms with the same denominator into a single term.

Function: CONTENT (p1, var1, ..., varn)
  returns a list whose first element is the greatest common divisor of the coefficients of the terms of the polynomial p1 in the variable varn (this is the content) and whose second element is the polynomial p1 divided by the content.

      (C1) CONTENT(2*X*Y+4*X**2*Y**2,Y);
      (D1)            [2*X, 2*X*Y**2+Y].

Function: DENOM (exp)
  returns the denominator of the rational expression exp.

Function: DIVIDE (p1, p2, var1, ..., varn)
  computes the quotient and remainder of the polynomial p1 divided by the polynomial p2, in a main polynomial variable, varn. The other variables are as in the RATVARS function. The result is a list whose first element is the quotient and whose second element is the remainder.

      (C1) DIVIDE(X+Y,X-Y,X);
      (D1)                        [1, 2 Y]
      (C2) DIVIDE(X+Y,X-Y);
      (D2)                      [ - 1, 2 X]

  (Note that Y is the main variable in C2)

Function: ELIMINATE ([eq1,eq2,...,eqn],[v1,v2,...,vk])
  eliminates variables from equations (or expressions assumed equal to zero) by taking successive resultants. This returns a list of n-k expressions with the k variables v1,...,vk eliminated. First v1 is eliminated yielding n-1 expressions, then v2 is, etc. If k=n then a single expression in a list is returned free of the variables v1,...,vk. In this case SOLVE is called to solve the last resultant for the last variable. Example:

      (C1) EXP1:2*X^2+Y*X+Z;
                                          2
      (D1)                   Z + X Y + 2 X
      (C2) EXP2:3*X+5*Y-Z-1;
      (D2)                - Z + 5 Y + 3 X - 1
      (C3) EXP3:Z^2+X-Y^2+5;
                             2    2
      (D3)                  Z  - Y  + X + 5
      (C4) ELIMINATE([EXP3,EXP2,EXP1],[Y,Z]);
                  8         7         6          5          4
      (D3) [7425 X  - 1170 X  + 1299 X  + 12076 X  + 22887 X
                                     3         2
                             - 5154 X  - 1291 X  + 7688 X + 15376]

Function: EZGCD (p1, p2, ...)
  gives a list whose first element is the g.c.d of the polynomials p1,p2,... and whose remaining elements are the polynomials divided by the g.c.d. This always uses the EZGCD algorithm.

Variable: FACEXPAND
  default: [TRUE] controls whether the irreducible factors returned by FACTOR are in expanded (the default) or recursive (normal CRE) form.

Function: FACTCOMB (exp)
  tries to combine the coefficients of factorials in exp with the factorials themselves by converting, for example, (N+1)*N! into (N+1)!. SUMSPLITFACT[TRUE] if set to FALSE will cause MINFACTORIAL to be applied after a FACTCOMB.

      (C1) (N+1)^B*N!^B;
                                            B   B
      (D1)                           (N + 1)  N!
      (C2) FACTCOMB(%);

Function: FACTOR (exp)
  factors the expression exp, containing any number of variables or functions, into factors irreducible over the integers. FACTOR(exp, p) factors exp over the field of integers with an element adjoined whose minimum polynomial is p. FACTORFLAG[FALSE] if FALSE suppresses the factoring of integer factors of rational expressions. DONTFACTOR may be set to a list of variables with respect to which factoring is not to occur. (It is initially empty). Factoring also will not take place with respect to any variables which are less important (using the variable ordering assumed for CRE form) than those on the DONTFACTOR list. SAVEFACTORS[FALSE] if TRUE causes the factors of an expression which is a product of factors to be saved by certain functions in order to speed up later factorizations of expressions containing some of the same factors. BERLEFACT[TRUE] if FALSE then the Kronecker factoring algorithm will be used otherwise the Berlekamp algorithm, which is the default, will be used. INTFACLIM[1000] is the largest divisor which will be tried when factoring a bignum integer. If set to FALSE (this is the case when the user calls FACTOR explicitly), or if the integer is a fixnum (i.e. fits in one machine word), complete factorization of the integer will be attempted. The user's setting of INTFACLIM is used for internal calls to FACTOR. Thus, INTFACLIM may be reset to prevent MACSYMA from taking an inordinately long time factoring large integers. NEWFAC[FALSE] may be set to true to use the new factoring routines. Do EXAMPLE(FACTOR); for examples.

Variable: FACTORFLAG
  default: [FALSE] if FALSE suppresses the factoring of integer factors of rational expressions.

Function: FACTOROUT (exp,var1,var2,...)
  rearranges the sum exp into a sum of terms of the form f(var1,var2,...)*g where g is a product of expressions not containing the vari's and f is factored.

Function: FACTORSUM (exp)
  tries to group terms in factors of exp which are sums into groups of terms such that their sum is factorable. It can recover the result of EXPAND((X+Y)^2+(Z+W)^2) but it can't recover EXPAND((X+1)^2+(X+Y)^2) because the terms have variables in common.

      (C1) (X+1)*((U+V)^2+A*(W+Z)^2),EXPAND;
            2      2                            2      2
      (D1) A X Z  + A Z  + 2 A W X Z + 2 A W Z + A W  X + V  X
                           2        2    2            2
              + 2 U V X + U  X + A W  + V  + 2 U V + U
      (C2) FACTORSUM(%);
                                         2          2
      (D2)                 (X + 1) (A (Z + W)  + (V + U) )

Function: FASTTIMES (p1, p2)
  multiplies the polynomials p1 and p2 by using a special algorithm for multiplication of polynomials. They should be multivariate, dense, and nearly the same size. Classical multiplication is of order N*M where N and M are the degrees. FASTTIMES is of order MAX(N,M)**1.585.

Function: FULLRATSIMP (exp)
  When non-rational expressions are involved, one call to RATSIMP followed as is usual by non-rational ("general") simplification may not be sufficient to return a simplified result. Sometimes, more than one such call may be necessary. The command FULLRATSIMP makes this process convenient. FULLRATSIMP repeatedly applies RATSIMP followed by non-rational simplification to an expression until no further change occurs. For example, consider For the expression EXP: (X^(A/2)+1)^2*(X^(A/2)-1)^2/(X^A-1) . RATSIMP(EXP); gives (X^(2*A)-2*X^A+1)/(X^A-1) . FULLRATSIMP(EXP); gives X^A-1 . The problem may be seen by looking at RAT(EXP); which gives ((X^(A/2))^4-2*(X^(A/2))^2+1)/(X^A-1) . FULLRATSIMP(exp,var1,...,varn) takes one or more arguments similar to RATSIMP and RAT.

Function: FULLRATSUBST (a,b,c)
  is the same as RATSUBST except that it calls itself recursively on its result until that result stops changing. This function is useful when the replacement expression and the replaced expression have one or more variables in common. FULLRATSUBST will also accept its arguments in the format of LRATSUBST. That is, the first argument may be a single substitution equation or a list of such equations, while the second argument is the expression being processed. There is a demo available by DEMO("lrats.dem"); .

Function: GCD (p1, p2, var1, ...)
  computes the greatest common divisor of p1 and p2. The flag GCD[SPMOD] determines which algorithm is employed. Setting GCD to EZ, EEZ, SUBRES, RED, or SPMOD selects the EZGCD, New EEZ GCD, subresultant PRS, reduced, or modular algorithm, respectively. If GCD:FALSE then GCD(p1,p2,var) will always return 1 for all var. Many functions (e.g. RATSIMP, FACTOR, etc.) cause gcd's to be taken implicitly. For homogeneous polynomials it is recommended that GCD:SUBRES be used. To take the gcd when an algebraic is present, e.g. GCD(X^2-2*SQRT(2)*X+2,X-SQRT(2)); , ALGEBRAIC must be TRUE and GCD must not be EZ. SUBRES is a new algorithm, and people who have been using the RED setting should probably change it to SUBRES. The GCD flag, default: [SPMOD], if FALSE will also prevent the greatest common divisor from being taken when expressions are converted to CRE form. This will sometimes speed the calculation if gcds are not required.

Function: GCDEX (f,g)
Function: GCDEX (f,g,var)
  returns a list containing [a,b,u] where u is the gcd of f and g, and u = a*f + b*g. The arguments f and g should b univariate polynomials, or else polynomials in VAR a supplied main variable since we need to be in a principal ideal domain for this to work. The gcd means the gcd regarding f and g as univariate polynomials with coefficients being rational functions in the other variables.

  The algorithm is simply the euclidean algorithm, where we have a sequence of `lis[i]:[a[i],b[i],r[i]] ..` which are all perpendicular to `[f,g,-1]` and the next one is built as if `q = quotient(r[i]/r[i+1])` then `lis[i+2]:lis[i]-q*lis[i+1]`, and it terminates at `lis[i+1]` when the remainder `r[i+2]` is zero.

      (C1) gcdex(x^2+1,x^3+4);

                                    2
                                   x  + 4 x - 1  x + 4
      (D1)/R/                   [- ------------, -----, 1]
                                        17        17

      (C2) d1.[x^2+1,x^3+4,-1];
      (D2)                                   0

  note that the gcd in the following is `1` since we work in `k(y)[x]`, not the `y+1` we would expect in `k[y,x]`

      (C4) gcdex(x*(y+1),y^2-1,x);

                                            1
      (D4)                            [0, ------, 1]
                                           2
                                          y  - 1

Function: GCFACTOR (n)
  factors the gaussian integer n over the gaussians, i.e. numbers of the form a + b i where a and b are rational integers (i.e. ordinary integers). Factors are normalized by making a and b non-negative.

Function: GFACTOR (exp)
  factors the polynomial exp over the Gaussian integers (i. e. with SQRT(-1) = %I adjoined). This is like FACTOR(exp,A**2+1) where A is %I.

      (C1)  GFACTOR(X**4-1);
      (D1)        (X - 1) (X + 1) (X + %I) (X - %I)

Function: GFACTORSUM (exp)
  is similar to FACTORSUM but applies GFACTOR instead of FACTOR.

Function: HIPOW (exp, v)
  the highest explicit exponent of v in exp. Sometimes it may be necessary to expand exp since this is not done automatically by HIPOW. Thus HIPOW(Y**3*X**2+X*Y**4,X) is 2.

Variable: INTFACLIM
  default: [1000] is the largest divisor which will be tried when factoring a bignum integer. If set to FALSE (this is the case when the user calls FACTOR explicitly), or if the integer is a fixnum (i.e. fits in one machine word), complete factorization of the integer will be attempted. The user's setting of INTFACLIM is used for internal calls to FACTOR. Thus, INTFACLIM may be reset to prevent MACSYMA from taking an inordinately long time factoring large integers.

Variable: KEEPFLOAT
  default: [FALSE] - if set to TRUE will prevent floating point numbers from being rationalized when expressions which contain them are converted to CRE form.

Function: LRATSUBST (list,exp)
  is analogous to SUBST(list_of_equations,exp) except that it uses RATSUBST instead of SUBST. The first argument of LRATSUBST must be an equation or a list of equations identical in format to that accepted by SUBST (see DESCRIBE(SUBST);). The substitutions are made in the order given by the list of equations, that is, from left to right. A demo is available by doing DEMO("lrats.dem"); .

Variable: MODULUS
  default: [FALSE] - if set to a positive prime p, then all arithmetic in the rational function routines will be done modulo p. That is all integers will be reduced to less than p/2 in absolute value (if p=2 then all integers are reduced to 1 or 0). This is the so called "balanced" modulus system, e.g. N MOD 5 = -2, -1, 0, 1, or 2. Warning: If EXP is already in CRE form when you reset MODULUS, then you may need to re-rat EXP, e.g. EXP:RAT(RATDISREP(EXP)), in order to get correct results. (If MODULUS is set to a positive non-prime integer, this setting will be accepted, but a warning will be given.)

Variable: NEWFAC
  default: [FALSE], if TRUE then FACTOR will use the new factoring routines.

Function: NUM (exp)
  obtains the numerator, exp1, of the rational expression exp = exp1/exp2.

Function: QUOTIENT (p1, p2, var1, ...)
  computes the quotient of the polynomial p1 divided by the polynomial p2.

Function: RAT (exp, v1, ..., vn)
  converts exp to CRE form by expanding and combining all terms over a common denominator and cancelling out the greatest common divisor of the numerator and denominator as well as converting floating point numbers to rational numbers within a tolerance of RATEPSILON[2.0E-8]. The variables are ordered according to the v1,...,vn as in RATVARS, if these are specified. RAT does not generally simplify functions other than + , - , * , / , and exponentiation to an integer power whereas RATSIMP does handle these cases. Note that atoms (numbers and names) in CRE form are not the same as they are in the general form. Thus RAT(X)- X results in RAT(0) which has a different internal representation than 0. RATFAC[FALSE] when TRUE invokes a partially factored form for CRE rational expressions. During rational operations the expression is maintained as fully factored as possible without an actual call to the factor package. This should always save space and may save some time in some computations. The numerator and denominator are still made relatively prime (e.g. RAT((X^2 -1)^4/(X+1)^2); yields (X-1)^4*(X+1)^2), but the factors within each part may not be relatively prime. RATPRINT[TRUE] if FALSE suppresses the printout of the message informing the user of the conversion of floating point numbers to rational numbers. KEEPFLOAT[FALSE] if TRUE prevents floating point numbers from being converted to rational numbers. (Also see the RATEXPAND and RATSIMP functions.)

      (C1) ((X-2*Y)**4/(X**2-4*Y**2)**2+1)*(Y+A)*(2*Y+X)
              /(4*Y**2+X**2);
                                                 4
                                        (X - 2 Y)
                    (Y + A) (2 Y + X) (------------ + 1)
                                         2      2 2
                                       (X  - 4 Y )
      (D1)          ------------------------------------
                                    2    2
                                 4 Y  + X
      (C2) RAT(%,Y,A,X);
                                  2 A + 2 Y
      (D2)/R/                     ---------
                                   X + 2 Y

Variable: RATALGDENOM
  default: [TRUE] - if TRUE allows rationalization of denominators wrt. radicals to take effect. To do this one must use CRE form in algebraic mode.

Function: RATCOEF (exp, v, n)
  returns the coefficient, C, of the expression v**n in the expression exp. n may be omitted if it is 1. C will be free (except possibly in a non-rational sense) of the variables in v. If no coefficient of this type exists, zero will be returned. RATCOEF expands and rationally simplifies its first argument and thus it may produce answers different from those of COEFF which is purely syntactic. Thus RATCOEF((X+1)/Y+X,X) returns (Y+1)/Y whereas COEFF returns 1. RATCOEF(exp,v,0), viewing exp as a sum, gives a sum of those terms which do not contain v. Therefore if v occurs to any negative powers, RATCOEF should not be used. Since exp is rationally simplified before it is examined, coefficients may not appear quite the way they were envisioned.

      (C1) S:A*X+B*X+5$
      (C2) RATCOEF(S,A+B);
      (D2)               X

Function: RATDENOM (exp)
  obtains the denominator of the rational expression exp. If exp is in general form then the DENOM function should be used instead, unless one wishes to get a CRE result.

Variable: RATDENOMDIVIDE
  default: [TRUE] - if FALSE will stop the splitting up of the terms of the numerator of RATEXPANDed expressions from occurring.

Function: RATDIFF (exp, var)
  differentiates the rational expression exp (which must be a ratio of polynomials or a polynomial in the variable var) with respect to var. For rational expressions this is much faster than DIFF. The result is left in CRE form. However, RATDIFF should not be used on factored CRE forms; use DIFF instead for such expressions.

      (C1) (4*X**3+10*X-11)/(X**5+5);
                                               3
                                            4 X  + 10 X - 11
      (D1)                                  ----------------
                                                  5
                                                 X
      (C2) MODULUS:3$
      (C3) MOD(D1);
                                      2
                                     X  + X - 1
      (D3)                      --------------------
                                 4    3    2
                                X  + X  + X  + X + 1
      (C4) RATDIFF(D1,X);
                                5    4    3
                               X  - X  - X  + X - 1
      (D4)                ------------------------------
                           8    7    5    4    3
                          X  - X  + X  - X  + X  - X + 1

Function: RATDISREP (exp)
  changes its argument from CRE form to general form. This is sometimes convenient if one wishes to stop the "contagion", or use rational functions in non-rational contexts. Most CRE functions will work on either CRE or non-CRE expressions, but the answers may take different forms. If RATDISREP is given a non-CRE for an argument, it returns its argument unchanged. See also TOTALDISREP.

Variable: RATEPSILON
  default: [2.0E-8] - the tolerance used in the conversion of floating point numbers to rational numbers.

Function: RATEXPAND (exp)
  expands exp by multiplying out products of sums and exponentiated sums, combining fractions over a common denominator, cancelling the greatest common divisor of the numerator and denominator, then splitting the numerator (if a sum) into its respective terms divided by the denominator. This is accomplished by converting exp to CRE form and then back to general form. The switch RATEXPAND, default: [FALSE], if TRUE will cause CRE expressions to be fully expanded when they are converted back to general form or displayed, while if it is FALSE then they will be put into a recursive form. (see RATSIMP) RATDENOMDIVIDE[TRUE] - if FALSE will stop the splitting up of the terms of the numerator of RATEXPANDed expressions from occurring. KEEPFLOAT[FALSE] if set to TRUE will prevent floating point numbers from being rationalized when expressions which contain them are converted to CRE form.

      (C1) RATEXPAND((2*X-3*Y)**3);
                      3         2       2        3
      (D1)      - 27 Y  + 54 X Y  - 36 X  Y + 8 X
      (C2) (X-1)/(X+1)**2+1/(X-1);
                                    X - 1       1
      (D2)                         -------- + -----
                                          2   X - 1
                                   (X + 1)
      (C3) EXPAND(D2);
                               X              1           1
      (D3)                ------------ - ------------ + -----
                           2              2             X - 1
                          X  + 2 X + 1   X  + 2 X + 1
      (C4) RATEXPAND(D2);
                                   2
                                2 X                 2
      (D4)                 --------------- + ---------------
                            3    2            3    2
                           X  + X  - X - 1   X  + X  - X - 1

Variable: RATFAC
  default: [FALSE] - when TRUE invokes a partially factored form for CRE rational expressions. During rational operations the expression is maintained as fully factored as possible without an actual call to the factor package. This should always save space and may save some time in some computations. The numerator and denominator are still made relatively prime, for example RAT((X^2 -1)^4/(X+1)^2); yields (X-1)^4*(X+1)^2), but the factors within each part may not be relatively prime. In the CTENSR (Component Tensor Manipulation) Package, if RATFAC is TRUE, it causes the Ricci, Einstein, Riemann, and Weyl tensors and the Scalar Curvature to be factored automatically. ** This should only be set for cases where the tensorial components are known to consist of few terms **. Note: The RATFAC and RATWEIGHT schemes are incompatible and may not both be used at the same time.

Function: RATNUMER (exp)
  obtains the numerator of the rational expression exp. If exp is in general form then the NUM function should be used instead, unless one wishes to get a CRE result.

Function: RATNUMP (exp)
  is TRUE if exp is a rational number (includes integers) else FALSE.

Function: RATP (exp)
  is TRUE if exp is in CRE or extended CRE form else FALSE.

Variable: RATPRINT
  default: [TRUE] - if FALSE suppresses the printout of the message informing the user of the conversion of floating point numbers to rational numbers.

Function: RATSIMP (exp)
  rationally" simplifies (similar to RATEXPAND) the expression exp and all of its subexpressions including the arguments to non- rational functions. The result is returned as the quotient of two polynomials in a recursive form, i.e. the coefficients of the main variable are polynomials in the other variables. Variables may, as in RATEXPAND, include non-rational functions (e.g. SIN(X**2+1) ) but with RATSIMP, the arguments to non-rational functions are rationally simplified. Note that RATSIMP is affected by some of the variables which affect RATEXPAND. RATSIMP(exp,v1,v2,...,vn) - enables rational simplification with the specification of variable ordering as in RATVARS. RATSIMPEXPONS[FALSE] - if TRUE will cause exponents of expressions to be RATSIMPed automatically during simplification.

      (C1) SIN(X/(X^2+X))=%E^((LOG(X)+1)**2-LOG(X)**2);
                                                 2          2
                          X          (LOG(X) + 1)  - LOG (X)
      (D1)          SIN(------) = %E
                         2
                        X  + X
      (C2) RATSIMP(%);
                                        1          2
      (D2)                        SIN(-----) = %E X
                                      X + 1
      (C3) ((X-1)**(3/2)-(X+1)*SQRT(X-1))/SQRT((X-1)*(X+1));
                             3/2
                      (X - 1)    - SQRT(X - 1) (X + 1)
      (D3)            --------------------------------
                          SQRT(X - 1) SQRT(X + 1)
      (C4) RATSIMP(%);
                                       2
      (D4)                      - -----------
                                  SQRT(X + 1)
      (C5)  X**(A+1/A),RATSIMPEXPONS:TRUE;
                          2
                         A  + 1
                         ------
                           A
      (D5)              X

Variable: RATSIMPEXPONS
  default: [FALSE] - if TRUE will cause exponents of expressions to be RATSIMPed automatically during simplification.

Function: RATSUBST (a, b, c)
  substitutes a for b in c. b may be a sum, product, power, etc. RATSUBST knows something of the meaning of expressions whereas SUBST does a purely syntactic substitution. Thus SUBST(A,X+Y,X+Y+Z) returns X+Y+Z whereas RATSUBST would return Z+A. RADSUBSTFLAG[FALSE] if TRUE permits RATSUBST to make substitutions like U for SQRT(X) in X. Do EXAMPLE(RATSUBST); for examples.

Function: RATVARS (var1, var2, ..., varn)
  forms its n arguments into a list in which the rightmost variable varn will be the main variable of future rational expressions in which it occurs, and the other variables will follow in sequence. If a variable is missing from the RATVARS list, it will be given lower priority than the leftmost variable var1. The arguments to RATVARS can be either variables or non-rational functions (e.g. SIN(X)). The variable RATVARS is a list of the arguments which have been given to this function.

Function: RATWEIGHT (v1, w1, ..., vn, wn)
  assigns a weight of wi to the variable vi. This causes a term to be replaced by 0 if its weight exceeds the value of the variable RATWTLVL [default is FALSE which means no truncation]. The weight of a term is the sum of the products of the weight of a variable in the term times its power. Thus the weight of 3*v1**2*v2 is 2*w1+w2. This truncation occurs only when multiplying or exponentiating CRE forms of expressions.

      (C5) RATWEIGHT(A,1,B,1);
      (D5)                         [[B, 1], [A, 1]]
      (C6) EXP1:RAT(A+B+1)$
      (C7) %**2;
                            2                  2
      (D7)/R/              B  + (2 A + 2) B + A  + 2 A + 1
      (C8) RATWTLVL:1$
      (C9) EXP1**2;
      (D9)/R/                       2 B + 2 A + 1

  Note: The RATFAC and RATWEIGHT schemes are incompatible and may not both be used at the same time.

Variable: RATWEIGHTS
  - a list of weight assignments (set up by the RATWEIGHT function), RATWEIGHTS; or RATWEIGHT(); will show you the list.

      KILL(...,RATWEIGHTS)

  and

      SAVE(...,RATWEIGHTS);

  both work.

Variable: RATWEYL
  default: [] - one of the switches controlling the simplification of components of the Weyl conformal tensor; if TRUE, then the components will be rationally simplified; if FACRAT is TRUE then the results will be factored as well.

Variable: RATWTLVL
  default: [FALSE] - used in combination with the RATWEIGHT function to control the truncation of rational (CRE form) expressions (for the default value of FALSE, no truncation occurs).

Function: REMAINDER (p1, p2, var1, ...)
  computes the remainder of the polynomial p1 divided by the polynomial p2.

Function: RESULTANT (p1, p2, var)
  computes the resultant of the two polynomials p1 and p2, eliminating the variable var. The resultant is a determinant of the coefficients of var in p1 and p2 which equals zero if and only if p1 and p2 have a non-constant factor in common. If p1 or p2 can be factored, it may be desirable to call FACTOR before calling RESULTANT. RESULTANT[SUBRES] - controls which algorithm will be used to compute the resultant. SUBRES for subresultant prs [the default], MOD for modular resultant algorithm, and RED for reduced prs. On most problems SUBRES should be best. On some large degree univariate or bivariate problems MOD may be better. Another alternative is the BEZOUT command which takes the same arguments as RESULTANT and returns a matrix. DETERMINANT of this matrix is the desired resultant.

Variable: SAVEFACTORS
  default: [FALSE] - if TRUE causes the factors of an expression which is a product of factors to be saved by certain functions in order to speed up later factorizations of expressions containing some of the same factors.

Function: SQFR (exp)
  is similar to FACTOR except that the polynomial factors are "square-free." That is, they have factors only of degree one. This algorithm, which is also used by the first stage of FACTOR, utilizes the fact that a polynomial has in common with its nth derivative all its factors of degree > n. Thus by taking gcds with the polynomial of the derivatives with respect to each variable in the polynomial, all factors of degree > 1 can be found.

      (C1) SQFR(4*X**4+4*X**3-3*X**2-4*X-1);
                                   2               2
      (D1)                       (X  - 1) (2 X + 1)

Function: TELLRAT (poly)
  adds to the ring of algebraic integers known to MACSYMA, the element which is the solution of the polynomial with integer coefficients. MACSYMA initially knows about %I and all roots of integers. TELLRAT(X); means substitute 0 for X in rational functions. There is a command UNTELLRAT which takes kernels and removes TELLRAT properties. When TELLRATing a multivariate polynomial, e.g. TELLRAT(X^2-Y^2);, there would be an ambiguity as to whether to substitute Y^2 for X^2 or vice versa. The system will pick a particular ordering, but if the user wants to specify which, e.g. TELLRAT(Y^2=X^2); provides a syntax which says replace Y^2 by X^2. TELLRAT and UNTELLRAT both can take any number of arguments, and TELLRAT(); returns a list of the current substitutions. Note: When you TELLRAT reducible polynomials, you want to be careful not to attempt to rationalize a denominator with a zero divisor. E.g. TELLRAT(W^3-1)$ ALGEBRAIC:TRUE$ RAT(1/(W^2-W)); will give "quotient by zero". This error can be avoided by setting RATALGDENOM:FALSE$. ALGEBRAIC[FALSE] must be set to TRUE in order for the simplification of algebraic integers to take effect. Do EXAMPLE(TELLRAT); for examples.

Function: TOTALDISREP (exp)
  converts every subexpression of exp from CRE to general form. If exp is itself in CRE form then this is identical to RATDISREP but if not then RATDISREP would return exp unchanged while TOTALDISREP would "totally disrep" it. This is useful for ratdisrepping expressions e.g., equations, lists, matrices, etc. which have some subexpressions in CRE form.

Function: UNTELLRAT (x)
  takes kernels and removes TELLRAT properties.

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