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Add scalar angle multiplication #815

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merged 2 commits into from
Oct 2, 2023
Merged

Add scalar angle multiplication #815

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1d23bda
Add scalar angle multiplication
cquiroz Oct 2, 2023
942b878
Implement PR suggestions
cquiroz Oct 2, 2023
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14 changes: 14 additions & 0 deletions modules/core/shared/src/main/scala/lucuma/core/math/Angle.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -300,6 +300,20 @@ object Angle extends AngleOptics {
def -(a: Angle): Angle =
Angle.fromMicroarcseconds(toMicroarcseconds - a.toMicroarcseconds)

/**
* Scalar multiplication of this angle and and natural number `a`. Exact
* @group Operations
*/
def *(a: Long): Angle =
Angle.fromMicroarcseconds(toMicroarcseconds * a)
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Unfortunately this overflows when a gets large. You may need to go to BigDecimal and renormalize it back into 0..360° before constructing the return value.

scala> Angle.Angle90 * 4000000
val res14: lucuma.core.math.Angle = 0
                                                                                                                                                                            
scala> Angle.Angle90 * 40000000
val res15: lucuma.core.math.Angle = 230290448384

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Thanks I pushed a new commit doing as you suggest and some tests


/**
* Scalar multiplication of this angle and double precission number `a`. Approximate
* @group Operations
*/
def *?(a: Double): Angle =
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I made it *? to denote that is approximate. not sure if it is a good idea, WDYT?

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We just document it when it's inexact. Pretty much anything involving Double is inexact by definition.

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I reverted to *

Angle.fromMicroarcseconds((toMicroarcseconds * a).toLong)

/**
* This angle as an Offset.P. Exact, invertible.
*
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19 changes: 19 additions & 0 deletions modules/tests/shared/src/test/scala/lucuma/core/math/AngleSuite.scala
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Expand Up @@ -182,4 +182,23 @@ final class AngleSuite extends munit.DisciplineSuite {
assertEquals(a.tan, scala.math.tan(a.toDoubleRadians))
}
}

test("Scalar int multiplication") {
assertEquals(Angle.Angle0 * 2, Angle.Angle0)
assertEquals(Angle.Angle90 * 2, Angle.Angle180)
assertEquals(Angle.Angle90 * 4, Angle.Angle0)
assertEquals(Angle.Angle90 * -2, Angle.Angle180)
assertEquals(Angle.Angle90 * 10, Angle.Angle180)
}

test("Scalar double multiplication") {
assertEquals(Angle.Angle0 *? 2, Angle.Angle0)
assertEquals(Angle.Angle90 *? 2, Angle.Angle180)
assertEquals(Angle.Angle90 *? 4, Angle.Angle0)
assertEquals(Angle.Angle90 *? -2, Angle.Angle180)
assertEquals(Angle.Angle90 *? 10, Angle.Angle180)
assertEquals(Angle.Angle180 *? 0.5, Angle.Angle90)
assert(((Angle.Angle180 *? 0.001) - Angle.fromDoubleDegrees(0.18)).toMicroarcseconds < 1000)
assert(((Angle.Angle180 *? -0.001) - Angle.fromDoubleDegrees(359.82)).toMicroarcseconds < 1000)
}
}
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