Fix erf by adding IrrationalConstants

Author: tansongchen

Project.toml

@@ -7,6 +7,7 @@ version = "0.2.1"
 ChainRules = "082447d4-558c-5d27-93f4-14fc19e9eca2"
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
 ChainRulesOverloadGeneration = "f51149dc-2911-5acf-81fc-2076a2a81d4f"
+IrrationalConstants = "92d709cd-6900-40b7-9082-c6be49f344b6"
 SliceMap = "82cb661a-3f19-5665-9e27-df437c7e54c8"
 SpecialFunctions = "276daf66-3868-5448-9aa4-cd146d93841b"
 SymbolicUtils = "d1185830-fcd6-423d-90d6-eec64667417b"
@@ -18,6 +19,7 @@ ChainRulesCore = "1"
 ChainRulesOverloadGeneration = "0.1"
 SliceMap = "0.2"
 SpecialFunctions = "2"
+IrrationalConstants = "0.2"
 SymbolicUtils = "1"
 Zygote = "0.6.55"
 julia = "1.6"

src/codegen.jl

@@ -1,5 +1,6 @@
 using ChainRulesCore
 using SpecialFunctions
+using IrrationalConstants: sqrtπ
 using SymbolicUtils, SymbolicUtils.Code
 using SymbolicUtils: BasicSymbolic, Pow
 
@@ -26,7 +27,7 @@ using SymbolicUtils: BasicSymbolic, Pow
 @scalar_rule asech(x::BasicSymbolic) inv(x * -sqrt(1 - x^2))
 @scalar_rule asinh(x::BasicSymbolic) inv(sqrt(x^2 + 1))
 @scalar_rule atanh(x::BasicSymbolic) inv(1 - x^2)
-@scalar_rule erf(x::BasicSymbolic) exp(-x^2)*(2 / sqrt(pi))
+@scalar_rule erf(x::BasicSymbolic) exp(-x^2) * 2/sqrtπ
 
 dummy = (NoTangent(), 1)
 @syms t₁