Removed negative infinity error handling

Value: [1e-5 to 1e-3]

packages/squiggle-lang/__tests__/Distributions/KlDivergence_test.res

@@ -2,7 +2,7 @@ open Jest
 open Expect
 open TestHelpers
 
-describe("kl divergence", () => {
+describe("kl divergence on continuous distributions", () => {
   let klDivergence = DistributionOperation.Constructors.klDivergence(~env)
   exception KlFailed
 
@@ -60,6 +60,48 @@ describe("kl divergence", () => {
   })
 })
 
+describe("kl divergence on discrete distributions", () => {
+  let klDivergence = DistributionOperation.Constructors.klDivergence(~env)
+  let mixture = a => DistributionTypes.DistributionOperation.Mixture(a)
+  exception KlFailed
+  exception MixtureFailed
+  let float1 = 1.0
+  let float2 = 2.0
+  let float3 = 3.0
+  let point1 = mkDirac(float1)
+  let point2 = mkDirac(float2)
+  let point3 = mkDirac(float3)
+  test("finite kl divergence", () => {
+    let answer = [(point1, 1e0), (point2, 1e0)]->mixture->run
+    let prediction = [(point1, 1e0), (point2, 1e0), (point3, 1e0)]->mixture->run
+    let kl = switch (prediction, answer) {
+    | (Dist(prediction'), Dist(answer')) => klDivergence(prediction', answer')
+    | _ => raise(MixtureFailed)
+    }
+    let analyticalKl = Js.Math.log(2.0 /. 3.0)
+    switch kl {
+    | Ok(kl') => kl'->expect->toBeCloseTo(analyticalKl)
+    | Error(err) =>
+      Js.Console.log(DistributionTypes.Error.toString(err))
+      raise(KlFailed)
+    }
+  })
+  test("infinite kl divergence", () => {
+    let prediction = [(point1, 1e0), (point2, 1e0)]->mixture->run
+    let answer = [(point1, 1e0), (point2, 1e0), (point3, 1e0)]->mixture->run
+    let kl = switch (prediction, answer) {
+    | (Dist(prediction'), Dist(answer')) => klDivergence(prediction', answer')
+    | _ => raise(MixtureFailed)
+    }
+    switch kl {
+    | Ok(kl') => kl'->expect->toEqual(neg_infinity)
+    | Error(err) =>
+      Js.Console.log(DistributionTypes.Error.toString(err))
+      raise(KlFailed)
+    }
+  })
+})
+
 describe("combine along support test", () => {
   // This tests the version of the function that we're NOT using. Haven't deleted the test in case we use the code later.
   test("combine along support test", _ => {
@@ -97,6 +139,7 @@ describe("combine along support test", () => {
             2.0 *. MagicNumbers.Epsilon.ten,
             1.0 -. MagicNumbers.Epsilon.ten,
             1.0,
+            1.0 +. MagicNumbers.Epsilon.ten,
           ],
           ys: [
             -0.34657359027997264,
@@ -104,6 +147,7 @@ describe("combine along support test", () => {
             -0.34657359027997264,
             -0.34657359027997264,
             -0.34657359027997264,
+            infinity,
           ],
         }),
       ),

packages/squiggle-lang/src/rescript/Distributions/PointSetDist/PointSetDist_Scoring.res

@@ -4,10 +4,9 @@ module KLDivergence = {
     float,
     Operation.Error.t,
   > =>
+    // We decided that negative infinity, not an error at answerElement = 0.0, is a desirable value.
     if answerElement == 0.0 {
       Ok(0.0)
-    } else if predictionElement == 0.0 {
-      Error(Operation.NegativeInfinityError)
     } else {
       let quot = predictionElement /. answerElement
       quot < 0.0 ? Error(Operation.ComplexNumberError) : Ok(-.answerElement *. logFn(quot))