SCALA - Computing Quandratics and Getting Complex numbers

Question

Just a quick question, I have a scala code which finds the roots of a quadratic equation. The problem I am having is printing out multiple answers and getting answers with complex numbers.

PS: I am in the first few weeks of my Scala course so I only know the bare basics.

val a = readDouble
val b = readDouble
val c = readDouble
if(b*b-4.*a*c > 0) //I have this to deal with the negatives :( {
val root1 = (-b + math.sqrt(b*b-4.*a*c)) / (2*a)
val root2 = (-b - math.sqrt(b*b-4.*a*c)) / (2*a)
println(root1 + " " root2)
}
else 
println("No root")

Thanks friend!

Answer 1

You should put your result in a Set, because:

• There can be multiple results, so it must be some collection
• You don't want to have duplicates and Set elimintates them for you

So something like this should work:

def roots(a : Double, b : Double, c: Double)= {
  if (b*b-4.0*a*c >= 0) {
     Set(1,-1).map(-b + _ * math.sqrt(b*b-4.0*a*c))
  }else{
     Set()
  }
}

val a = readDouble
val b = readDouble
val c = readDouble

println(roots(a,b,c))

With this function, you can get the following results:

scala> roots(2,3,4)
res4: scala.collection.immutable.Set[_ <: Double] = Set()

scala> roots(-2,3,4)
res5: scala.collection.immutable.Set[_ <: Double] = Set(3.4031242374328485, -9.403124237432849)

scala> roots(2,0,0)
res6: scala.collection.immutable.Set[_ <: Double] = Set(0.0)

For complex numbers, you can use spire. Just change the code above a little bit:

import spire.implicits._
import spire.math._

def roots(a : Complex[Double], b : Complex[Double], c: Complex[Double]) =
     Set(1,-1).map(-b + _ * (b*b-4.0*a*c).sqrt)