From 1ba3690764e90aa6f7bcb3cb1e095475d40e3d91 Mon Sep 17 00:00:00 2001
From: xuri <xuri.me@gmail.com>
Date: Tue, 14 Sep 2021 22:23:12 +0800
Subject: new formula functions: WEIBULL and WEIBULL.DIST, ref #65

---
 calc.go      | 42 ++++++++++++++++++++++++++++++++++++++++++
 calc_test.go | 40 ++++++++++++++++++++++++++++------------
 2 files changed, 70 insertions(+), 12 deletions(-)

diff --git a/calc.go b/calc.go
index fa6ec0a..9cbc8ec 100644
--- a/calc.go
+++ b/calc.go
@@ -504,6 +504,8 @@ type formulaFuncs struct {
 //    VAR.P
 //    VARP
 //    VLOOKUP
+//    WEIBULL
+//    WEIBULL.DIST
 //    XOR
 //    YEAR
 //    Z.TEST
@@ -5614,6 +5616,46 @@ func (fn *formulaFuncs) VARdotP(argsList *list.List) formulaArg {
 	return fn.VARP(argsList)
 }
 
+// WEIBULL function calculates the Weibull Probability Density Function or the
+// Weibull Cumulative Distribution Function for a supplied set of parameters.
+// The syntax of the function is:
+//
+//    WEIBULL(x,alpha,beta,cumulative)
+//
+func (fn *formulaFuncs) WEIBULL(argsList *list.List) formulaArg {
+	if argsList.Len() != 4 {
+		return newErrorFormulaArg(formulaErrorVALUE, "WEIBULL requires 4 arguments")
+	}
+	x := argsList.Front().Value.(formulaArg).ToNumber()
+	alpha := argsList.Front().Next().Value.(formulaArg).ToNumber()
+	beta := argsList.Back().Prev().Value.(formulaArg).ToNumber()
+	if alpha.Type == ArgNumber && beta.Type == ArgNumber && x.Type == ArgNumber {
+		if alpha.Number < 0 || alpha.Number <= 0 || beta.Number <= 0 {
+			return newErrorFormulaArg(formulaErrorNA, formulaErrorNA)
+		}
+		cumulative := argsList.Back().Value.(formulaArg).ToBool()
+		if cumulative.Boolean && cumulative.Number == 1 {
+			return newNumberFormulaArg(1 - math.Exp(0-math.Pow((x.Number/beta.Number), alpha.Number)))
+		}
+		return newNumberFormulaArg((alpha.Number / math.Pow(beta.Number, alpha.Number)) *
+			math.Pow(x.Number, (alpha.Number-1)) * math.Exp(0-math.Pow((x.Number/beta.Number), alpha.Number)))
+	}
+	return newErrorFormulaArg(formulaErrorVALUE, formulaErrorVALUE)
+}
+
+// WEIBULLdotDIST function calculates the Weibull Probability Density Function
+// or the Weibull Cumulative Distribution Function for a supplied set of
+// parameters. The syntax of the function is:
+//
+//    WEIBULL.DIST(x,alpha,beta,cumulative)
+//
+func (fn *formulaFuncs) WEIBULLdotDIST(argsList *list.List) formulaArg {
+	if argsList.Len() != 4 {
+		return newErrorFormulaArg(formulaErrorVALUE, "WEIBULL.DIST requires 4 arguments")
+	}
+	return fn.WEIBULL(argsList)
+}
+
 // ZdotTEST function calculates the one-tailed probability value of the
 // Z-Test. The syntax of the function is:
 //
diff --git a/calc_test.go b/calc_test.go
index 7018ee9..763ea1f 100644
--- a/calc_test.go
+++ b/calc_test.go
@@ -858,6 +858,12 @@ func TestCalcCellValue(t *testing.T) {
 		"=VARP(A1:A5)": "1.25",
 		// VAR.P
 		"=VAR.P(A1:A5)": "1.25",
+		// WEIBULL
+		"=WEIBULL(1,3,1,FALSE)":  "1.103638323514327",
+		"=WEIBULL(2,5,1.5,TRUE)": "0.985212776817482",
+		// WEIBULL.DIST
+		"=WEIBULL.DIST(1,3,1,FALSE)":  "1.103638323514327",
+		"=WEIBULL.DIST(2,5,1.5,TRUE)": "0.985212776817482",
 		// Information Functions
 		// ISBLANK
 		"=ISBLANK(A1)": "FALSE",
@@ -1899,20 +1905,30 @@ func TestCalcCellValue(t *testing.T) {
 		// VAR.P
 		"=VAR.P()":     "VAR.P requires at least 1 argument",
 		"=VAR.P(\"\")": "#DIV/0!",
+		// WEIBULL
+		"=WEIBULL()":               "WEIBULL requires 4 arguments",
+		"=WEIBULL(\"\",1,1,FALSE)": "#VALUE!",
+		"=WEIBULL(1,0,1,FALSE)":    "#N/A",
+		"=WEIBULL(1,1,-1,FALSE)":   "#N/A",
+		// WEIBULL.DIST
+		"=WEIBULL.DIST()":               "WEIBULL.DIST requires 4 arguments",
+		"=WEIBULL.DIST(\"\",1,1,FALSE)": "#VALUE!",
+		"=WEIBULL.DIST(1,0,1,FALSE)":    "#N/A",
+		"=WEIBULL.DIST(1,1,-1,FALSE)":   "#N/A",
 		// Z.TEST
-		"Z.TEST(A1)":        "Z.TEST requires at least 2 arguments",
-		"Z.TEST(A1,0,0,0)":  "Z.TEST accepts at most 3 arguments",
-		"Z.TEST(H1,0)":      "#N/A",
-		"Z.TEST(A1,\"\")":   "strconv.ParseFloat: parsing \"\": invalid syntax",
-		"Z.TEST(A1,1)":      "#DIV/0!",
-		"Z.TEST(A1,1,\"\")": "strconv.ParseFloat: parsing \"\": invalid syntax",
+		"=Z.TEST(A1)":        "Z.TEST requires at least 2 arguments",
+		"=Z.TEST(A1,0,0,0)":  "Z.TEST accepts at most 3 arguments",
+		"=Z.TEST(H1,0)":      "#N/A",
+		"=Z.TEST(A1,\"\")":   "strconv.ParseFloat: parsing \"\": invalid syntax",
+		"=Z.TEST(A1,1)":      "#DIV/0!",
+		"=Z.TEST(A1,1,\"\")": "strconv.ParseFloat: parsing \"\": invalid syntax",
 		// ZTEST
-		"ZTEST(A1)":        "ZTEST requires at least 2 arguments",
-		"ZTEST(A1,0,0,0)":  "ZTEST accepts at most 3 arguments",
-		"ZTEST(H1,0)":      "#N/A",
-		"ZTEST(A1,\"\")":   "strconv.ParseFloat: parsing \"\": invalid syntax",
-		"ZTEST(A1,1)":      "#DIV/0!",
-		"ZTEST(A1,1,\"\")": "strconv.ParseFloat: parsing \"\": invalid syntax",
+		"=ZTEST(A1)":        "ZTEST requires at least 2 arguments",
+		"=ZTEST(A1,0,0,0)":  "ZTEST accepts at most 3 arguments",
+		"=ZTEST(H1,0)":      "#N/A",
+		"=ZTEST(A1,\"\")":   "strconv.ParseFloat: parsing \"\": invalid syntax",
+		"=ZTEST(A1,1)":      "#DIV/0!",
+		"=ZTEST(A1,1,\"\")": "strconv.ParseFloat: parsing \"\": invalid syntax",
 		// Information Functions
 		// ISBLANK
 		"=ISBLANK(A1,A2)": "ISBLANK requires 1 argument",
-- 
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