Function realNum

src/compute-engine/rubi/rubi-utils.ts:115–123

real machine value of an expression, or null if not a real number

(e: Expression)

      // The general form Subst[u, expr, v] := u /. expr -> v replaces the
      // subexpression `expr` (a non-variable, e.g. the expanded log argument
      // c·dⁿ·(e+f·x)^{m·n}) with `v` — used by the 6 "power-in-log" /
      // radical back-substitution rules (1.1.3.1 #44/#45, 1.1.3.2 #103/#104,
      // 3.2.2 #15, 3.3 #60). Dispatching on args[1] here is essential:
      // substituting ctx.x for those compound middles rewrites `x` itself and
      // corrupts the antiderivative (spurious powers in the log argument).
      const target = build(args[1], ctx);
      if (target.symbol === ctx.x) return u.subs({ [ctx.x]: v }).evaluate();
      return replaceSubexpr(u, target, v).evaluate();
    }
    case 'Rational':
      // NOTE: ce.number() does not accept a MathJSON array (spins) — box
      return ce.expr(json as any);