[Libreoffice-commits] core.git: Branch 'libreoffice-5-0' - sc/source

[Dennis Francis]

 sc/source/core/tool/interpr5.cxx |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

New commits:
commit 26b38babf9a85caac32019cd86e2307b446743c7
Author: Dennis Francis <dennisfrancis.in at gmail.com>
Date:   Fri Oct 23 03:28:37 2015 +0530

    tdf#32834 : improve the precision of MDETERM calculation
    
    MDETERM uses lcl_LUP_decompose() which as the name suggests does LUP decomposition.
    This patch allows additive cancellations to occur in a cleaner way while doing the *only*
    additive operation in LUP decomposition, that is while computing Shur complement.
    This patch does not change the high level semantics of the algorithm.
    Also note that this change makes improvement only in the case where matrix elements entered
    by the user are *integers*. The change allows MDETERM to evaluate to exact 0.0 for
    singular integer matrices.
    
    The steps to calculate Shur complement are :
    
    for i = k+1 to n
      aik = aik / akk;
      for j = k+1 to n
        aij = aij - akj*aik
    
    This is now modified as :
    
    for i = k+1 to n
      for j = k+1 to n
        aij = ( aij*akk - akj*aik ) / akk
    
    Without this change MDETERM() for certain singular matrices used to evaluate to a tiny non zero value,
    which also caused MINVERSE() to generate a wrong output.
    An example of such a matrix is :
    1 2 3
    4 5 6
    7 8 9
    
    Change-Id: Idd4211ddceab1b758fd05bfd57f7eecd5d4fd1a0
    Reviewed-on: https://gerrit.libreoffice.org/19534
    Reviewed-by: Eike Rathke <erack at redhat.com>
    Tested-by: Eike Rathke <erack at redhat.com>
    (cherry picked from commit e1e73a97b20af862f2fb914cb16a4f74c3ad31cb)
    Reviewed-on: https://gerrit.libreoffice.org/19578

diff --git a/sc/source/core/tool/interpr5.cxx b/sc/source/core/tool/interpr5.cxx
index bfaa438..3947eba 100644
--- a/sc/source/core/tool/interpr5.cxx
+++ b/sc/source/core/tool/interpr5.cxx
@@ -709,11 +709,12 @@ static int lcl_LUP_decompose( ScMatrix* mA, const SCSIZE n,
         // Compute Schur complement.
         for (SCSIZE i = k+1; i < n; ++i)
         {
-            double fTmp = mA->GetDouble( k, i) / mA->GetDouble( k, k);
-            mA->PutDouble( fTmp, k, i);
+            double fNum = mA->GetDouble( k, i);
+            double fDen = mA->GetDouble( k, k);
+            mA->PutDouble( fNum/fDen, k, i);
             for (SCSIZE j = k+1; j < n; ++j)
-                mA->PutDouble( mA->GetDouble( j, i) - fTmp * mA->GetDouble( j,
-                            k), j, i);
+                mA->PutDouble( ( mA->GetDouble( j, i) * fDen  -
+                            fNum * mA->GetDouble( j, k) ) / fDen, j, i);
         }
     }
 #if OSL_DEBUG_LEVEL > 1