From 08866f1331c67087e3792d127fe4180bcc0577cf Mon Sep 17 00:00:00 2001
From: Koustav Chowdhury <kc99.kol@gmail.com>
Date: Fri, 12 Jul 2019 11:16:40 +0530
Subject: [PATCH] math : add error and gamma functions; sort all functions

---
 vlib/math/math.v      | 55 +++++++++++++++++++++++++++++--------------
 vlib/math/math_test.v | 14 +++++++++++
 2 files changed, 51 insertions(+), 18 deletions(-)

diff --git a/vlib/math/math.v b/vlib/math/math.v
index 6eb27b55cc..e81bb3aa9c 100644
--- a/vlib/math/math.v
+++ b/vlib/math/math.v
@@ -90,6 +90,11 @@ pub fn cosh(a f64) f64 {
 	return C.cosh(a)
 }
 
+// degrees convert from degrees to radians.
+pub fn degrees(radians f64) f64 {
+	return radians * (180.0 / Pi)
+}
+
 // exp calculates exponement of the number (math.pow(math.E, a)).
 pub fn exp(a f64) f64 {
 	return C.exp(a)
@@ -110,11 +115,33 @@ pub fn digits(n, base int) []int {
 	return res
 }
 
+// erf computes the error funtion value
+pub fn erf(a f64) f64 {
+	return C.erf(a)
+}
+
+// erfc computes the complimentary error function value
+pub fn erfc(a f64) f64 {
+	return C.erfc(a)
+}
+
 // exp2 returns the base-2 exponential function of a (math.pow(2, a)).
 pub fn exp2(a f64) f64 {
 	return C.exp2(a)
 }
 
+// factorial calculates the factorial of the provided value.
+pub fn factorial(a int) i64 {
+	if a < 0 {
+		panic('factorial: Cannot find factorial of negative number')
+	}
+	mut prod := 1
+	for i:= 0; i < a; i++ {
+		prod *= (i+1)
+	}
+	return prod
+}
+
 // floor returns the nearest integer equal or lower of the provided value.
 pub fn floor(a f64) f64 {
 	return C.floor(a)
@@ -125,6 +152,11 @@ pub fn fmod(a, b f64) f64 {
 	return C.fmod(a, b)
 }
 
+// gamma computes the gamma function value
+pub fn gamma(a f64) f64 {
+	return C.tgamma(a)
+}
+
 // gcd calculates greatest common (positive) divisor (or zero if a and b are both zero).
 pub fn gcd(a, b i64) i64 {
 	if a < 0 {
@@ -170,6 +202,11 @@ pub fn log10(a f64) f64 {
 	return C.log10(a)
 }
 
+// log_gamma computes the log-gamma function value
+pub fn log_gamma(a f64) f64 {
+	return C.lgamma(a)
+}
+
 // log_n calculates base-N logarithm of the provided value.
 pub fn log_n(a, b f64) f64 {
 	return C.log(a) / C.log(b)
@@ -201,11 +238,6 @@ pub fn radians(degrees f64) f64 {
 	return degrees * (Pi / 180.0)
 }
 
-// degrees convert from degrees to radians.
-pub fn degrees(radians f64) f64 {
-	return radians * (180.0 / Pi)
-}
-
 // round returns the integer nearest to the provided value.
 pub fn round(f f64) f64 {
 	return C.round(f)
@@ -240,16 +272,3 @@ pub fn tanh(a f64) f64 {
 pub fn trunc(a f64) f64 {
 	return C.trunc(a)
 }
-
-// factorial calculates the factorial of the provided value.
-pub fn factorial(a int) i64 {
-	if a < 0 {
-		panic('factorial: Cannot find factorial of negative number')
-	}
-	mut prod := 1
-	for i:= 0; i < a; i++ {
-		prod *= (i+1)
-	}
-	return prod
-}
-
diff --git a/vlib/math/math_test.v b/vlib/math/math_test.v
index deacf99e4a..c3030aeeaa 100644
--- a/vlib/math/math_test.v
+++ b/vlib/math/math_test.v
@@ -31,3 +31,17 @@ fn test_factorial() {
 	assert math.factorial(5) == 120
 	assert math.factorial(0) == 1
 }
+
+fn test_erf() {
+	assert math.erf(0) == 0
+	assert math.erf(1.5) + math.erf(-1.5) == 0
+	assert math.erfc(0) == 1
+	assert math.erf(2.5) + math.erfc(2.5) == 1
+	assert math.erfc(3.6) + math.erfc(-3.6) == 2
+}
+
+fn test_gamma() {
+	assert math.gamma(1) == 1
+	assert math.gamma(5) == 24
+	assert math.log_gamma(4.5) == math.log(math.gamma(4.5))
+}