Function polyDivideX

src/compute-engine/rubi/rubi-utils.ts:369–402

(
  P: Expression,
  L: Expression,
  x: string
)

      return monomialsX(ex, x);
    }
    case 'Multiply': {
      let acc: [Expression, number][] = [[ce.One, 0]];
      for (const f of ops) {
        const m = monomialsX(f, x);
        if (m === null) return null;
        const next: [Expression, number][] = [];
        for (const [c1, d1] of acc)
          for (const [c2, d2] of m) next.push([c1.mul(c2), d1 + d2]);
        if (next.length > 256) return null;
        acc = next;
      }
      return acc;
    }
  }
  return null;
}

/** ascending coefficient array, or null if not a polynomial in x */
export function polyCoeffsX(u: Expression, x: string): Expression[] | null {
  const ce = u.engine;
  const ms = monomialsX(u, x);
  if (ms === null) return null;
  const deg = ms.reduce((m, [, d]) => Math.max(m, d), 0);
  const coeffs: Expression[] = new Array(deg + 1).fill(ce.Zero);
  for (const [c, d] of ms) coeffs[d] = coeffs[d].add(c);
  return coeffs.map((c) => c.evaluate());
}

/** effective degree after dropping provably-zero leading coefficients */
function trimZeros(coeffs: Expression[]): Expression[] {
  let last = coeffs.length - 1;
  while (last > 0 && zeroQ(coeffs[last])) last--;
  return coeffs.slice(0, last + 1);
}

/** long division P / L over symbolic coefficients → [quotient, remainder] */
export function polyDivideX(