Math F# snippets (#7789)

Author: albert-du

snippets/fsharp/System/Decimal/Round/fs.fsproj

@@ -4,9 +4,16 @@
     <TargetFramework>net6.0</TargetFramework>
   </PropertyGroup>
   <ItemGroup>
-    <Compile Include="Round1.fs" />
-    <Compile Include="Round12.fs" />
+    <Compile Include="mean1.fs" />
     <Compile Include="midpoint1.fs" />
+    <Compile Include="midpoint2.fs" />
     <Compile Include="mpr.fs" />
+    <Compile Include="precision1.fs" />
+    <Compile Include="precision2.fs" />
+    <Compile Include="Round1.fs" />
+    <Compile Include="Round12.fs" />
+    <Compile Include="Round12.fs" />
+    <Compile Include="single1.fs" />
+    <Compile Include="source.fs" />
   </ItemGroup>
 </Project>

snippets/fsharp/System/Decimal/Round/mean1.fs

@@ -0,0 +1,33 @@
+module mean1
+
+// <Snippet2>
+open System
+
+let values = [| 1.15m; 1.25m; 1.35m; 1.45m; 1.55m; 1.65m |]
+let mutable sum = 0m
+
+// Calculate true mean.
+for value in values do
+    sum <- sum + value
+
+printfn $"True mean:     {sum / decimal values.Length:N2}"
+
+// Calculate mean with rounding away from zero.
+sum <- 0m
+for value in values do
+    sum <- sum + Math.Round(value, 1, MidpointRounding.AwayFromZero)
+
+printfn $"AwayFromZero:  {sum / decimal values.Length:N2}"
+
+// Calculate mean with rounding to nearest.
+sum <- 0m
+for value in values do
+    sum <- sum + Math.Round(value, 1, MidpointRounding.ToEven)
+
+printfn $"ToEven:        {sum / decimal values.Length:N2}"
+
+// The example displays the following output:
+//       True mean:     1.40
+//       AwayFromZero:  1.45
+//       ToEven:        1.40
+// </Snippet2>

snippets/fsharp/System/Decimal/Round/midpoint2.fs

@@ -0,0 +1,32 @@
+module midpoint2
+
+// <Snippet6>
+open System
+
+let values = 
+    [| 12.; 12.1; 12.2; 12.3; 12.4; 12.5
+       12.6; 12.7; 12.8; 12.9; 13. |]
+
+printfn "%-10s %-10s %-10s %-15s %-15s" "Value" "Default" "ToEven" "AwayFromZero" "ToZero"
+
+for value in values do
+    $"{value,-10:R} {Math.Round(value),-10} " +
+    $"{Math.Round(value, MidpointRounding.ToEven),-10} " +
+    $"{Math.Round(value, MidpointRounding.AwayFromZero),-15} " +
+    $"{Math.Round(value, MidpointRounding.ToZero),-15}"
+    |> printfn "%s"
+    
+// The example displays the following output:
+//       Value      Default    ToEven     AwayFromZero    ToZero
+//       12         12         12         12              12
+//       12.1       12         12         12              12
+//       12.2       12         12         12              12
+//       12.3       12         12         12              12
+//       12.4       12         12         12              12
+//       12.5       12         12         13              12
+//       12.6       13         13         13              12
+//       12.7       13         13         13              12
+//       12.8       13         13         13              12
+//       12.9       13         13         13              12
+//       13         13         13         13              13
+// </Snippet6>

snippets/fsharp/System/Decimal/Round/precision1.fs

@@ -0,0 +1,32 @@
+module precision1
+
+// <Snippet7>
+open System
+
+let roundValueAndAdd (value: double) =
+    printfn $"{value,5:N1} {value,20:R}  {Math.Round(value, MidpointRounding.ToEven),12} {Math.Round(value, MidpointRounding.AwayFromZero),15}"
+    value + 0.1
+
+printfn "%5s %20s  %12s %15s\n" "Value" "Full Precision" "ToEven" "AwayFromZero"
+let mutable value = 11.1
+for _ = 0 to 5 do
+    value <- roundValueAndAdd value
+
+printfn ""
+
+value <- 11.5
+roundValueAndAdd value
+|> ignore
+
+// The example displays the following output:
+//       Value       Full Precision        ToEven    AwayFromZero
+//
+//        11.1                 11.1            11              11
+//        11.2                 11.2            11              11
+//        11.3   11.299999999999999            11              11
+//        11.4   11.399999999999999            11              11
+//        11.5   11.499999999999998            11              11
+//        11.6   11.599999999999998            12              12
+//
+//        11.5                 11.5            12              12
+// </Snippet7>

snippets/fsharp/System/Decimal/Round/precision2.fs

@@ -0,0 +1,58 @@
+module precision2
+
+// <Snippet8>
+open System
+
+let roundApproximate dbl digits margin mode =
+    let fraction = dbl * Math.Pow(10, digits)
+    let value = Math.Truncate fraction
+    let fraction = fraction - value
+    if fraction = 0 then
+        dbl
+    else
+        let tolerance = margin * dbl
+        // Determine whether this is a midpoint value.
+        if (fraction >= 0.5 - tolerance) && (fraction <= 0.5 + tolerance) then
+            if mode = MidpointRounding.AwayFromZero then
+                (value + 1.) / Math.Pow(10, digits)
+            elif value % 2. <> 0 then
+                (value + 1.) / Math.Pow(10, digits)
+            else
+                value / Math.Pow(10, digits)
+        // Any remaining fractional value greater than .5 is not a midpoint value.
+        elif fraction > 0.5 then
+            (value + 1.) / Math.Pow(10, digits)
+        else
+            value / Math.Pow(10, digits)
+
+
+let roundValueAndAdd value =
+    let tolerance = 8e-14
+    let round = roundApproximate value 0 tolerance
+
+    printfn $"{value,5:N1} {value,20:R}  {round MidpointRounding.ToEven,12} {round MidpointRounding.AwayFromZero,15}"
+    value + 0.1
+
+printfn "%5s %20s  %12s %15s\n" "Value" "Full Precision" "ToEven" "AwayFromZero"
+let mutable value = 11.1
+for _ = 0 to 5 do
+    value <- roundValueAndAdd value
+
+printfn ""
+
+value <- 11.5
+roundValueAndAdd value 
+|> ignore
+
+// The example displays the following output:
+//       Value       Full Precision        ToEven    AwayFromZero
+//
+//        11.1                 11.1            11              11
+//        11.2                 11.2            11              11
+//        11.3   11.299999999999999            11              11
+//        11.4   11.399999999999999            11              11
+//        11.5   11.499999999999998            12              12
+//        11.6   11.599999999999998            12              12
+//
+//        11.5                 11.5            12              12
+// </Snippet8>

snippets/fsharp/System/Decimal/Round/single1.fs

@@ -0,0 +1,27 @@
+module single1
+
+// <Snippet1>
+// In F#, 'float', 'float64', and 'double' are aliases for System.Double...
+// 'float32' and 'single' are aliases for System.Single
+open System
+
+let value = 16.325f
+printfn $"Widening Conversion of {value:R} (type {value.GetType().Name}) to {double value:R} (type {(double value).GetType().Name}): "
+printfn $"{Math.Round(decimal value, 2)}"
+printfn $"{Math.Round(decimal value, 2, MidpointRounding.AwayFromZero)}"
+printfn ""
+
+let decValue = decimal value
+printfn $"Cast of {value:R} (type {value.GetType().Name}) to {decValue} (type {decValue.GetType().Name}): "
+printfn $"{Math.Round(decValue, 2)}"
+printfn $"{Math.Round(decValue, 2, MidpointRounding.AwayFromZero)}"
+
+// The example displays the following output:
+//    Widening Conversion of 16.325 (type Single) to 16.325000762939453 (type Double):
+//    16.33
+//    16.33
+//
+//    Cast of 16.325 (type Single) to 16.325 (type Decimal):
+//    16.32
+//    16.33
+// </Snippet1>

snippets/fsharp/System/Decimal/Round/source.fs

@@ -0,0 +1,23 @@
+module source
+
+// <Snippet3>
+open System
+
+printfn 
+    $"""{Math.Round(3.44m, 1)}
+{Math.Round(3.45m, 1)}
+{Math.Round(3.46m, 1)}
+
+{Math.Round(4.34m, 1)}
+{Math.Round(4.35m, 1)}
+{Math.Round(4.36m, 1)}"""
+
+// The example displays the following output:
+//       3.4
+//       3.4
+//       3.5
+//
+//       4.3
+//       4.4
+//       4.4
+// </Snippet3>

snippets/fsharp/System/Math/Abs/Abs1.fs

@@ -0,0 +1,20 @@
+module Abs1
+
+// <Snippet1>
+open System
+
+let decimals = 
+    [ Decimal.MaxValue; 12.45M; 0M
+      -19.69M; Decimal.MinValue ]
+
+for value in decimals do
+    // The 'abs' function may be used instead.
+    printfn $"Abs({value}) = {Math.Abs value}"
+
+// The example displays the following output:
+//       Abs(79228162514264337593543950335) = 79228162514264337593543950335
+//       Abs(12.45) = 12.45
+//       Abs(0) = 0
+//       Abs(-19.69) = 19.69
+//       Abs(-79228162514264337593543950335) = 79228162514264337593543950335
+// </Snippet1>

snippets/fsharp/System/Math/Abs/abs2.fs

@@ -0,0 +1,22 @@
+module abs2
+
+// <Snippet2>
+open System
+
+let doubles = 
+    [ Double.MaxValue; 16.354e-17; 15.098123; 0
+      -19.069713; -15.058e18; Double.MinValue ]
+
+for value in doubles do
+    // The 'abs' function may be used instead.
+    printfn $"Abs({value}) = {Math.Abs value}"
+
+// The example displays the following output:
+//       Abs(1.79769313486232E+308) = 1.79769313486232E+308
+//       Abs(1.6354E-16) = 1.6354E-16
+//       Abs(15.098123) = 15.098123
+//       Abs(0) = 0
+//       Abs(-19.069713) = 19.069713
+//       Abs(-1.5058E+19) = 1.5058E+19
+//       Abs(-1.79769313486232E+308) = 1.79769313486232E+308
+// </Snippet2>

snippets/fsharp/System/Math/Abs/abs3.fs

@@ -0,0 +1,22 @@
+module abs3
+
+// <Snippet3>
+open System
+
+let values = 
+    [ Int16.MaxValue; 10328s; 0s; -1476s; Int16.MinValue ]
+
+for value in values do
+    try
+        // The 'abs' function may be used instead.
+        printfn $"Abs({value}) = {Math.Abs value}"
+    with :? OverflowException ->
+        printfn $"Unable to calculate the absolute value of {value}."
+
+// The example displays the following output:
+//       Abs(32767) = 32767
+//       Abs(10328) = 10328
+//       Abs(0) = 0
+//       Abs(-1476) = 1476
+//       Unable to calculate the absolute value of -32768.
+// </Snippet3>