Merge pull request #355 from quantified-uncertainty/commutative-error

Fix subtraction not commuting under pointsets

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

@@ -9,6 +9,7 @@ describe("Combining Continuous and Discrete Distributions", () => {
         #Multiply,
         {xs: [0., 1.], ys: [1., 1.]},
         {xs: [-1.], ys: [1.]},
+        ~discretePosition=Second,
       ),
     ), // Multiply distribution by -1
     true,

packages/squiggle-lang/__tests__/ReducerInterface/ReducerInterface_Distribution_test.res

@@ -54,6 +54,7 @@ describe("eval on distribution functions", () => {
   describe("subtract", () => {
     testEval("10 - normal(5, 1)", "Ok(Normal(5,1))")
     testEval("normal(5, 1) - 10", "Ok(Normal(-5,1))")
+    testEval("mean(1 - toPointSet(normal(5, 2)))", "Ok(-4.002309896304692)")
   })
   describe("multiply", () => {
     testEval("normal(10, 2) * 2", "Ok(Normal(20,4))")

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

@@ -187,16 +187,20 @@ let toDiscretePointMassesFromDiscrete = (s: PointSetTypes.xyShape): pointMassesW
   {n: n, masses: masses, means: means, variances: variances}
 }
 
+type argumentPosition = First | Second
+
 let combineShapesContinuousDiscrete = (
   op: Operation.convolutionOperation,
   continuousShape: PointSetTypes.xyShape,
   discreteShape: PointSetTypes.xyShape,
+  ~discretePosition: argumentPosition,
 ): PointSetTypes.xyShape => {
   let t1n = continuousShape |> XYShape.T.length
   let t2n = discreteShape |> XYShape.T.length
 
   // each x pair is added/subtracted
-  let fn = Operation.Convolution.toFn(op)
+  let opFunc = Operation.Convolution.toFn(op)
+  let fn = discretePosition == First ? (a, b) => opFunc(b, a) : opFunc
 
   let outXYShapes: array<array<(float, float)>> = Belt.Array.makeUninitializedUnsafe(t2n)
 
@@ -207,9 +211,13 @@ let combineShapesContinuousDiscrete = (
       // creates a new continuous shape for each one of the discrete points, and collects them in outXYShapes.
       let dxyShape: array<(float, float)> = Belt.Array.makeUninitializedUnsafe(t1n)
       for i in 0 to t1n - 1 {
+        // When this operation is flipped (like 1 - normal(5, 2)) then the
+        // x axis coordinates would all come out the wrong order. So we need
+        // to fill them out in the opposite direction
+        let index = discretePosition == First ? t1n - 1 - i : i
         Belt.Array.set(
           dxyShape,
-          i,
+          index,
           (
             fn(continuousShape.xs[i], discreteShape.xs[j]),
             continuousShape.ys[i] *. discreteShape.ys[j],

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

@@ -278,6 +278,7 @@ let combineAlgebraicallyWithDiscrete = (
   op: Operation.convolutionOperation,
   t1: t,
   t2: PointSetTypes.discreteShape,
+  ~discretePosition: AlgebraicShapeCombination.argumentPosition,
 ) => {
   let t1s = t1 |> getShape
   let t2s = t2.xyShape // TODO would like to use Discrete.getShape here, but current file structure doesn't allow for that
@@ -294,6 +295,7 @@ let combineAlgebraicallyWithDiscrete = (
       op,
       continuousAsLinear |> getShape,
       t2s,
+      ~discretePosition,
     )
 
     let combinedIntegralSum = switch op {

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

@@ -277,8 +277,18 @@ let combineAlgebraically = (op: Operation.convolutionOperation, t1: t, t2: t): t
   // continuous (*) continuous => continuous, but also
   // discrete (*) continuous => continuous (and vice versa). We have to take care of all combos and then combine them:
   let ccConvResult = Continuous.combineAlgebraically(op, t1.continuous, t2.continuous)
-  let dcConvResult = Continuous.combineAlgebraicallyWithDiscrete(op, t2.continuous, t1.discrete)
-  let cdConvResult = Continuous.combineAlgebraicallyWithDiscrete(op, t1.continuous, t2.discrete)
+  let dcConvResult = Continuous.combineAlgebraicallyWithDiscrete(
+    op,
+    t2.continuous,
+    t1.discrete,
+    ~discretePosition=First,
+  )
+  let cdConvResult = Continuous.combineAlgebraicallyWithDiscrete(
+    op,
+    t1.continuous,
+    t2.discrete,
+    ~discretePosition=Second,
+  )
   let continuousConvResult = Continuous.sum([ccConvResult, dcConvResult, cdConvResult])
 
   // ... finally, discrete (*) discrete => discrete, obviously:

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

@@ -46,9 +46,20 @@ let combineAlgebraically = (op: Operation.convolutionOperation, t1: t, t2: t): t
   switch (t1, t2) {
   | (Continuous(m1), Continuous(m2)) =>
     Continuous.combineAlgebraically(op, m1, m2) |> Continuous.T.toPointSetDist
-  | (Continuous(m1), Discrete(m2))
-  | (Discrete(m2), Continuous(m1)) =>
-    Continuous.combineAlgebraicallyWithDiscrete(op, m1, m2) |> Continuous.T.toPointSetDist
+  | (Discrete(m1), Continuous(m2)) =>
+    Continuous.combineAlgebraicallyWithDiscrete(
+      op,
+      m2,
+      m1,
+      ~discretePosition=First,
+    ) |> Continuous.T.toPointSetDist
+  | (Continuous(m1), Discrete(m2)) =>
+    Continuous.combineAlgebraicallyWithDiscrete(
+      op,
+      m1,
+      m2,
+      ~discretePosition=Second,
+    ) |> Continuous.T.toPointSetDist
   | (Discrete(m1), Discrete(m2)) =>
     Discrete.combineAlgebraically(op, m1, m2) |> Discrete.T.toPointSetDist
   | (m1, m2) => Mixed.combineAlgebraically(op, toMixed(m1), toMixed(m2)) |> Mixed.T.toPointSetDist