resolved fdo#65082 RATE function should not find roots <= -1

Limit RATE to roots > -1.0, which is what also Excel and now Gnumeric
do. If the Newton goal seek fails for the default guess value 0.1 try
other values.

This now also calculates the few remaining error cases of i#15090
attachment https://issues.apache.org/ooo/attachment.cgi?id=6528
correctly.

Change-Id: Ic62cc807626b4715035c3076f58f303b9020db5a
(cherry picked from commit 9ee7be4efb494351c4be096ffa04cdbd85cdc3d4)
Reviewed-on: https://gerrit.libreoffice.org/4328
Reviewed-by: Noel Power <noel.power@suse.com>
Tested-by: Noel Power <noel.power@suse.com>

1 files changed, 46 insertions, 13 deletions

diff --git a/sc/source/core/tool/interpr2.cxx b/sc/source/core/tool/interpr2.cxx
index dc843591e9ba..29845cd728e1 100644
--- a/sc/source/core/tool/interpr2.cxx
+++ b/sc/source/core/tool/interpr2.cxx
@@ -1430,16 +1430,19 @@ bool ScInterpreter::RateIteration( double fNper, double fPayment, double fPv,
                     fXnew = fX + 1.1 * SCdEpsilon;  // move away from zero slope
                 else
                     fXnew = fX - fTerm / fTermDerivation;
-            nCount++;
-            // more accuracy not possible in oscillating cases
-            bFound = (fabs(fXnew - fX) < SCdEpsilon);
-            fX = fXnew;
+                nCount++;
+                // more accuracy not possible in oscillating cases
+                bFound = (fabs(fXnew - fX) < SCdEpsilon);
+                fX = fXnew;
             }
         }
         // Gnumeric returns roots < -1, Excel gives an error in that cases,
         // ODFF says nothing about it. Enable the statement, if you want Excel's
-        // behavior
+        // behavior.
         //bValid =(fX >=-1.0);
+        // Update 2013-06-17: Gnumeric (v1.12.2) doesn't return roots <= -1
+        // anymore.
+        bValid = (fX > -1.0);
     }
     else
     { // Nper is not an integer value.
@@ -1466,11 +1469,11 @@ bool ScInterpreter::RateIteration( double fNper, double fPayment, double fPv,
                     fXnew = fX + 1.1 * SCdEpsilon;  // move away from zero slope
                 else
                     fXnew = fX - fTerm / fTermDerivation;
-            nCount++;
-             // more accuracy not possible in oscillating cases
-            bFound = (fabs(fXnew - fX) < SCdEpsilon);
-            fX = fXnew;
-            bValid = (fX >= -1.0);  // otherwise pow(1.0+fX,fNper) will fail
+                nCount++;
+                // more accuracy not possible in oscillating cases
+                bFound = (fabs(fXnew - fX) < SCdEpsilon);
+                fX = fXnew;
+                bValid = (fX >= -1.0);  // otherwise pow(1.0+fX,fNper) will fail
             }
         }
     }
@@ -1484,14 +1487,18 @@ void ScInterpreter::ScZins()
     RTL_LOGFILE_CONTEXT_AUTHOR( aLogger, "sc", "er", "ScInterpreter::ScZins" );
     double fPv, fPayment, fNper;
     // defaults for missing arguments, see ODFF spec
-    double fFv = 0, fPayType = 0, fGuess = 0.1;
+    double fFv = 0, fPayType = 0, fGuess = 0.1, fOrigGuess = 0.1;
     bool bValid = true;
+    bool bDefaultGuess = true;
     nFuncFmtType = NUMBERFORMAT_PERCENT;
     sal_uInt8 nParamCount = GetByte();
     if ( !MustHaveParamCount( nParamCount, 3, 6 ) )
         return;
     if (nParamCount == 6)
-        fGuess = GetDouble();
+    {
+        fOrigGuess = fGuess = GetDouble();
+        bDefaultGuess = false;
+    }
     if (nParamCount >= 5)
         fPayType = GetDouble();
     if (nParamCount >= 4)
@@ -1509,7 +1516,33 @@ void ScInterpreter::ScZins()
     //if (fPayType != 0.0) fPayType = 1.0;
     bValid = RateIteration(fNper, fPayment, fPv, fFv, fPayType, fGuess);
     if (!bValid)
-        SetError(errNoConvergence);
+    {
+        /* TODO: try also for specified guess values, not only default? As is,
+         * a specified 0.1 guess may be error result but a default 0.1 guess
+         * may succeed. On the other hand, using a different guess value than
+         * the specified one may not be desired, even if that didn't match. */
+        if (bDefaultGuess)
+        {
+            /* TODO: this is rather ugly, instead of looping over different
+             * guess values and doing a Newton goal seek for each we could
+             * first insert the values into the RATE equation to obtain a set
+             * of y values and then do a bisecting goal seek, possibly using
+             * different algorithms. */
+            double fX = fOrigGuess;
+            for (int nStep = 2; nStep <= 10 && !bValid; ++nStep)
+            {
+                fGuess = fX * nStep;
+                bValid = RateIteration( fNper, fPayment, fPv, fFv, fPayType, fGuess);
+                if (!bValid)
+                {
+                    fGuess = fX / nStep;
+                    bValid = RateIteration( fNper, fPayment, fPv, fFv, fPayType, fGuess);
+                }
+            }
+        }
+        if (!bValid)
+            SetError(errNoConvergence);
+    }
     PushDouble(fGuess);
 }