compute exponential e high precision value / published by https://github.com/dacr/code-examples-manager #cd88fb58-3717-4528-88f1-b3286c541cd2/b5b8ae7e39fc80648c15b9861c223e78a37f3579

math-e.sc

// summary : compute exponential e high precision value
// keywords : scala, math, e, math, mathcontext, precision, scale, @testable
// publish : gist
// authors : David Crosson
// license : Apache NON-AI License Version 2.0 (https://raw.githubusercontent.com/non-ai-licenses/non-ai-licenses/main/NON-AI-APACHE2)
// id : cd88fb58-3717-4528-88f1-b3286c541cd2
// created-on : 2021-02-09T08:58:06Z
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// ---------------------
//> using scala  "3.3.0"
//> using dep "org.scalatest::scalatest:3.2.16"
//> using objectWrapper
// ---------------------

import org.scalatest._
import flatspec._
import matchers._

import scala.math.BigDecimal.RoundingMode
import scala.math._


def e(iter:Int):BigDecimal = {
  val from = BigDecimal(1, java.math.MathContext.UNLIMITED)
  LazyList
    .iterate( (1, from, BigDecimal(1)) ) { case (n, result, fact) =>
      val newFact = fact * n
      val newResult = result + 1/newFact
      (n+1, newResult, newFact)
    }.collect {case (n, result, _) if iter == n => result}
    .head
}


class ETest extends AnyFlatSpec with should.Matchers {
  override def suiteName: String = "FactTest"

  "e" should "return the right result" in {
      e(20).toDouble shouldBe E
  }
  it should "give high precision value" in {
    val computed = e(2000).setScale(5000, RoundingMode.FLOOR)
    info(computed.toString)
  }
}

org.scalatest.tools.Runner.main(Array("-oDF", "-s", classOf[ETest].getName))