Function interval

src/compute-engine/numerics/interval.ts:38–95

(expr: Expression)

}

export function interval(expr: Expression): Interval | undefined {
  if (isFunction(expr, 'Interval')) {
    let op1: Expression = expr.op1;
    let op2: Expression = expr.op2;
    let openStart = false;
    let openEnd = false;
    if (isFunction(op1, 'Open')) {
      openStart = true;
      op1 = op1.op1;
    } else if (isFunction(op1, 'Closed')) {
      op1 = op1.op1;
    }

    if (isFunction(op2, 'Open')) {
      openEnd = true;
      op2 = op2.op1;
    } else if (isFunction(op2, 'Closed')) {
      op2 = op2.op1;
    }

    const start = op1.N();
    const end = op2.N();

    if (!isNumber(start) || !isNumber(end)) return undefined;

    return { start: start.re, openStart, end: end.re, openEnd };
  }

  //
  // Known sets which are also intervals...
  //
  if (isSymbol(expr)) {
    if (expr.symbol === 'EmptySet')
      return { start: 0, openStart: true, end: 0, openEnd: true };

    if (expr.symbol === 'RealNumbers')
      return {
        start: -Infinity,
        openStart: false,
        end: Infinity,
        openEnd: false,
      };

    if (expr.symbol === 'NegativeNumbers')
      return { start: -Infinity, openStart: false, end: 0, openEnd: true };

    if (expr.symbol === 'NonPositiveNumbers')
      return { start: -Infinity, openStart: false, end: 0, openEnd: false };

    if (expr.symbol === 'PositiveNumbers')
      return { start: 0, openStart: true, end: Infinity, openEnd: false };

    if (expr.symbol === 'NonNegativeNumbers')
      return { start: 0, openStart: false, end: Infinity, openEnd: false };
  }

  return undefined;
}