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## 88 Package ratpow

The package `ratpow` provides functions that return the coefficients of the numerator of a CRE polynomial in a given variable.

For example,

- `ratp_coeffs(5*x^7-3*x^2+4,x)` returns `[[7,5],[2,-3],[0,4]]`, which omits zero terms;
- `ratp_dense_coeffs(5*x^7-y*x^2+4,x)` returns `[5,0,0,0,0,-y,0,4]`, which includes zero terms;
- `ratp_dense_coeffs((x^4-y^4)/(x-y),x)` returns `[1,y,y^2,y^3]`, because CRE simplifies the expression to `x^3+y*x^2+y^2*x+y^3`;
- `ratp_dense_coeffs(x+sqrt(x),x)` returns `[1,sqrt(x)]` while `ratp_dense_coeffs(x+sqrt(x),sqrt(x))` returns `[1,x]`: in CRE form, `x` and `sqrt(x)` are treated as independent variables.

The returned coefficients are in CRE form except for numbers.

For the list of vars of a CRE polynomial, use `showratvars`. For the denominator of a CRE polynomial, use `ratdenom`.

For information about CREs see also `rat`, `ratdisrep` and `showratvars`.

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### 88.1 Functions and Variables for ratpow

Function: ratp_hipow (expr, x)

  Returns the highest power of x in `ratnumer(expr)`

      (%i1) load("ratpow")$

      (%i2) ratp_hipow( x^(5/2) + x^2 , x);
      (%o2)                           2

      (%i3) ratp_hipow( x^(5/2) + x^2 , sqrt(x));
      (%o3)                           5

  Categories: Rational expressions · Package ratpow ·

Function: ratp_lopow (expr, x)

  Returns the lowest power of x in `ratnumer(expr)`

      (%i1) load("ratpow")$

      (%i2) ratp_lopow( x^5 + x^2 , x);
      (%o2)                           2

  The following example returns 0 since `1` equals `x^0`:

      (%i1) load("ratpow")$

      (%i2) ratp_lopow( x^5 + x^2 + 1, x);
      (%o2)                           0

  The CRE form of the following equation contains `sqrt(x)` and `x`. Since they are interpreted as independent variables, `ratp_lopow` returns `0`:

      (%i1) load("ratpow")$

      (%i2) g:sqrt(x)^5 + sqrt(x)^2;
                                   5/2
      (%o2)                       x    + x

      (%i3) showratvars(g);
                                    1/2
      (%o3)                       [x   , x]

      (%i4) ratp_lopow( g, x);
      (%o4)                           0

      (%i5) ratp_lopow( g, sqrt(x));
      (%o5)                           0

  Categories: Rational expressions · Package ratpow ·

Function: ratp_coeffs (expr, x)

  Returns the powers and coefficients of x in `ratnumer(expr)` as a list of length-2 lists; returned coefficients are in CRE form except for numbers.

  `ratnumer(expr)`.

      (%i1) load("ratpow")$

      (%i2) ratp_coeffs( 4*x^3 + x + sqrt(x), x);
      (%o2)/R/         [[3, 4], [1, 1], [0, sqrt(x)]]

  Categories: Rational expressions · Package ratpow ·

Function: ratp_dense_coeffs (expr, x)

  Returns the coefficients of powers of x in `ratnumer(expr)` from highest to lowest; returned coefficients are in CRE form except for numbers.

      (%i1) load("ratpow")$

      (%i2) ratp_dense_coeffs( 4*x^3 + x + sqrt(x), x);
      (%o2)/R/               [4, 0, 1, sqrt(x)]

  Categories: Rational expressions · Package ratpow ·

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