Add implementation of RATE from patch in bug #52050

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1186111 13f79535-47bb-0310-9956-ffa450edef68

src/documentation/content/xdocs/status.xml

@@ -34,6 +34,7 @@
 
     <changes>
         <release version="3.8-beta5" date="2011-??-??">
+           <action dev="poi-developers" type="add">52050 - Support for the Excel RATE function</action>
            <action dev="poi-developers" type="fix">51566 - HSLF fix for finishing parsing the picture stream on the first non-valid type</action>
            <action dev="poi-developers" type="fix">51974 - Avoid HWPF issue when identifying the picture type</action>
            <action dev="poi-developers" type="fix">52035 - Fix signed issue with very large word 6 files</action>

src/java/org/apache/poi/ss/formula/eval/FunctionEval.java

@@ -102,6 +102,7 @@ public final class FunctionEval {
 		retval[58] = FinanceFunction.NPER;
 		retval[59] = FinanceFunction.PMT;
 
+      retval[60] = new Rate();
 		retval[62] = new Irr();
 		retval[63] = NumericFunction.RAND;
 		retval[64] = new Match();

src/java/org/apache/poi/ss/formula/functions/Rate.java

@@ -0,0 +1,119 @@
+/* ====================================================================
+   Licensed to the Apache Software Foundation (ASF) under one or more
+   contributor license agreements.  See the NOTICE file distributed with
+   this work for additional information regarding copyright ownership.
+   The ASF licenses this file to You under the Apache License, Version 2.0
+   (the "License"); you may not use this file except in compliance with
+   the License.  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+==================================================================== */
+
+package org.apache.poi.ss.formula.functions;
+
+import org.apache.poi.ss.formula.eval.ErrorEval;
+import org.apache.poi.ss.formula.eval.EvaluationException;
+import org.apache.poi.ss.formula.eval.NumberEval;
+import org.apache.poi.ss.formula.eval.OperandResolver;
+import org.apache.poi.ss.formula.eval.ValueEval;
+
+/**
+ * Implements the Excel Rate function
+ */
+public class Rate implements Function {
+   public ValueEval evaluate(ValueEval[] args, int srcRowIndex, int srcColumnIndex) {
+      if (args.length < 3) { //First 3 parameters are mandatory
+         return ErrorEval.VALUE_INVALID;
+      }
+
+      double periods, payment, present_val, future_val = 0, type = 0, estimate = 0.1, rate;
+
+      try {
+         ValueEval v1 = OperandResolver.getSingleValue(args[0], srcRowIndex, srcColumnIndex);
+         ValueEval v2 = OperandResolver.getSingleValue(args[1], srcRowIndex, srcColumnIndex);
+         ValueEval v3 = OperandResolver.getSingleValue(args[2], srcRowIndex, srcColumnIndex);
+         ValueEval v4 = null;
+         if (args.length >= 4)
+            v4 = OperandResolver.getSingleValue(args[3], srcRowIndex, srcColumnIndex);
+         ValueEval v5 = null;
+         if (args.length >= 5)
+            v5 = OperandResolver.getSingleValue(args[4], srcRowIndex, srcColumnIndex);
+         ValueEval v6 = null;
+         if (args.length >= 6)
+            v6 = OperandResolver.getSingleValue(args[5], srcRowIndex, srcColumnIndex);
+
+         periods = OperandResolver.coerceValueToDouble(v1); 
+         payment = OperandResolver.coerceValueToDouble(v2);
+         present_val = OperandResolver.coerceValueToDouble(v3);
+         if (args.length >= 4)
+            future_val = OperandResolver.coerceValueToDouble(v4);
+         if (args.length >= 5)
+            type = OperandResolver.coerceValueToDouble(v5);
+         if (args.length >= 6)
+            estimate = OperandResolver.coerceValueToDouble(v6);
+         rate = calculateRate(periods, payment, present_val, future_val, type, estimate) ;
+
+         checkValue(rate);
+      } catch (EvaluationException e) {
+         e.printStackTrace() ;
+         return e.getErrorEval();
+      }
+
+      return new NumberEval( rate ) ;
+   }
+
+   private double calculateRate(double nper, double pmt, double pv, double fv, double type, double guess) {
+      //FROM MS http://office.microsoft.com/en-us/excel-help/rate-HP005209232.aspx
+      int FINANCIAL_MAX_ITERATIONS = 20;//Bet accuracy with 128
+      double FINANCIAL_PRECISION = 0.0000001;//1.0e-8
+
+      double y, y0, y1, x0, x1 = 0, f = 0, i = 0;
+      double rate = guess;
+      if (Math.abs(rate) < FINANCIAL_PRECISION) {
+         y = pv * (1 + nper * rate) + pmt * (1 + rate * type) * nper + fv;
+      } else {
+         f = Math.exp(nper * Math.log(1 + rate));
+         y = pv * f + pmt * (1 / rate + type) * (f - 1) + fv;
+      }
+      y0 = pv + pmt * nper + fv;
+      y1 = pv * f + pmt * (1 / rate + type) * (f - 1) + fv;
+
+      // find root by Newton secant method
+      i = x0 = 0.0;
+      x1 = rate;
+      while ((Math.abs(y0 - y1) > FINANCIAL_PRECISION) && (i < FINANCIAL_MAX_ITERATIONS)) {
+         rate = (y1 * x0 - y0 * x1) / (y1 - y0);
+         x0 = x1;
+         x1 = rate;
+
+         if (Math.abs(rate) < FINANCIAL_PRECISION) {
+            y = pv * (1 + nper * rate) + pmt * (1 + rate * type) * nper + fv;
+         } else {
+            f = Math.exp(nper * Math.log(1 + rate));
+            y = pv * f + pmt * (1 / rate + type) * (f - 1) + fv;
+         }
+
+         y0 = y1;
+         y1 = y;
+         ++i;
+      }
+      return rate;
+   }
+
+   /**
+    * Excel does not support infinities and NaNs, rather, it gives a #NUM! error in these cases
+    * 
+    * @throws EvaluationException (#NUM!) if <tt>result</tt> is <tt>NaN</> or <tt>Infinity</tt>
+    */
+   static final void checkValue(double result) throws EvaluationException {
+      if (Double.isNaN(result) || Double.isInfinite(result)) {
+         throw new EvaluationException(ErrorEval.NUM_ERROR);
+      }
+   }
+}