diff --git a/src/PhpSpreadsheet/Calculation/Calculation.php b/src/PhpSpreadsheet/Calculation/Calculation.php
index a1e1585d..8a2b74ad 100644
--- a/src/PhpSpreadsheet/Calculation/Calculation.php
+++ b/src/PhpSpreadsheet/Calculation/Calculation.php
@@ -2782,7 +2782,7 @@ class Calculation
      *
      * @param string $formula Formula to parse
      *
-     * @return array
+     * @return array|bool
      */
     public function parseFormula($formula)
     {
@@ -4278,6 +4278,8 @@ class Calculation
             throw new Exception($errorMessage);
         }
         trigger_error($errorMessage, E_USER_ERROR);
+
+        return false;
     }
 
     /**
@@ -4305,6 +4307,8 @@ class Calculation
             $aReferences = Coordinate::extractAllCellReferencesInRange($pRange);
             $pRange = $pSheetName . '!' . $pRange;
             if (!isset($aReferences[1])) {
+                $currentCol = '';
+                $currentRow = 0;
                 //    Single cell in range
                 sscanf($aReferences[0], '%[A-Z]%d', $currentCol, $currentRow);
                 if ($pSheet->cellExists($aReferences[0])) {
@@ -4315,6 +4319,8 @@ class Calculation
             } else {
                 // Extract cell data for all cells in the range
                 foreach ($aReferences as $reference) {
+                    $currentCol = '';
+                    $currentRow = 0;
                     // Extract range
                     sscanf($reference, '%[A-Z]%d', $currentCol, $currentRow);
                     if ($pSheet->cellExists($reference)) {
diff --git a/src/PhpSpreadsheet/Cell/Coordinate.php b/src/PhpSpreadsheet/Cell/Coordinate.php
index 1bca6f44..12e3b689 100644
--- a/src/PhpSpreadsheet/Cell/Coordinate.php
+++ b/src/PhpSpreadsheet/Cell/Coordinate.php
@@ -339,6 +339,9 @@ abstract class Coordinate
         //    Sort the result by column and row
         $sortKeys = [];
         foreach (array_unique($returnValue) as $coord) {
+            $column = '';
+            $row = 0;
+
             sscanf($coord, '%[A-Z]%d', $column, $row);
             $sortKeys[sprintf('%3s%09d', $column, $row)] = $coord;
         }
diff --git a/src/PhpSpreadsheet/Chart/Renderer/JpGraph.php b/src/PhpSpreadsheet/Chart/Renderer/JpGraph.php
index 63ea91b2..ec3f6e8a 100644
--- a/src/PhpSpreadsheet/Chart/Renderer/JpGraph.php
+++ b/src/PhpSpreadsheet/Chart/Renderer/JpGraph.php
@@ -134,6 +134,7 @@ class JpGraph implements IRenderer
 
     private function percentageSumCalculation($groupID, $seriesCount)
     {
+        $sumValues = [];
         //    Adjust our values to a percentage value across all series in the group
         for ($i = 0; $i < $seriesCount; ++$i) {
             if ($i == 0) {
@@ -614,8 +615,9 @@ class JpGraph implements IRenderer
         for ($groupID = 0; $groupID < $iLimit; ++$groupID) {
             $grouping = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotGrouping();
             $exploded = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotStyle();
+            $datasetLabels = [];
             if ($groupID == 0) {
-                $labelCount = count($this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotValuesByIndex(0)->getPointCount());
+                $labelCount = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotValuesByIndex(0)->getPointCount();
                 if ($labelCount > 0) {
                     $datasetLabels = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotCategoryByIndex(0)->getDataValues();
                     $datasetLabels = $this->formatDataSetLabels($groupID, $datasetLabels, $labelCount);
diff --git a/src/PhpSpreadsheet/Collection/Cells.php b/src/PhpSpreadsheet/Collection/Cells.php
index ac5faf04..b87b805e 100644
--- a/src/PhpSpreadsheet/Collection/Cells.php
+++ b/src/PhpSpreadsheet/Collection/Cells.php
@@ -153,6 +153,8 @@ class Cells
     {
         $sortKeys = [];
         foreach ($this->getCoordinates() as $coord) {
+            $column = '';
+            $row = 0;
             sscanf($coord, '%[A-Z]%d', $column, $row);
             $sortKeys[sprintf('%09d%3s', $row, $column)] = $coord;
         }
@@ -172,15 +174,16 @@ class Cells
         $col = ['A' => '1A'];
         $row = [1];
         foreach ($this->getCoordinates() as $coord) {
+            $c = '';
+            $r = 0;
             sscanf($coord, '%[A-Z]%d', $c, $r);
             $row[$r] = $r;
             $col[$c] = strlen($c) . $c;
         }
-        if (!empty($row)) {
-            // Determine highest column and row
-            $highestRow = max($row);
-            $highestColumn = substr(max($col), 1);
-        }
+
+        // Determine highest column and row
+        $highestRow = max($row);
+        $highestColumn = substr(max($col), 1);
 
         return [
             'row' => $highestRow,
@@ -205,6 +208,9 @@ class Cells
      */
     public function getCurrentColumn()
     {
+        $column = '';
+        $row = 0;
+
         sscanf($this->currentCoordinate, '%[A-Z]%d', $column, $row);
 
         return $column;
@@ -217,6 +223,9 @@ class Cells
      */
     public function getCurrentRow()
     {
+        $column = '';
+        $row = 0;
+
         sscanf($this->currentCoordinate, '%[A-Z]%d', $column, $row);
 
         return (int) $row;
@@ -240,6 +249,9 @@ class Cells
 
         $columnList = [1];
         foreach ($this->getCoordinates() as $coord) {
+            $c = '';
+            $r = 0;
+
             sscanf($coord, '%[A-Z]%d', $c, $r);
             if ($r != $row) {
                 continue;
@@ -268,6 +280,9 @@ class Cells
 
         $rowList = [0];
         foreach ($this->getCoordinates() as $coord) {
+            $c = '';
+            $r = 0;
+
             sscanf($coord, '%[A-Z]%d', $c, $r);
             if ($c != $column) {
                 continue;
@@ -336,6 +351,9 @@ class Cells
     public function removeRow($row)
     {
         foreach ($this->getCoordinates() as $coord) {
+            $c = '';
+            $r = 0;
+
             sscanf($coord, '%[A-Z]%d', $c, $r);
             if ($r == $row) {
                 $this->delete($coord);
@@ -351,6 +369,9 @@ class Cells
     public function removeColumn($column)
     {
         foreach ($this->getCoordinates() as $coord) {
+            $c = '';
+            $r = 0;
+
             sscanf($coord, '%[A-Z]%d', $c, $r);
             if ($c == $column) {
                 $this->delete($coord);
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/Chart.php b/src/PhpSpreadsheet/Reader/Xlsx/Chart.php
index 641d6d1c..2b920d70 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/Chart.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/Chart.php
@@ -278,6 +278,7 @@ class Chart
                     break;
                 case 'ser':
                     $marker = null;
+                    $seriesIndex = '';
                     foreach ($seriesDetails as $seriesKey => $seriesDetail) {
                         switch ($seriesKey) {
                             case 'idx':
@@ -433,7 +434,7 @@ class Chart
     private static function parseRichText(SimpleXMLElement $titleDetailPart)
     {
         $value = new RichText();
-
+        $objText = null;
         foreach ($titleDetailPart as $titleDetailElementKey => $titleDetailElement) {
             if (isset($titleDetailElement->t)) {
                 $objText = $value->createTextRun((string) $titleDetailElement->t);
diff --git a/src/PhpSpreadsheet/ReferenceHelper.php b/src/PhpSpreadsheet/ReferenceHelper.php
index c423b840..54bc182a 100644
--- a/src/PhpSpreadsheet/ReferenceHelper.php
+++ b/src/PhpSpreadsheet/ReferenceHelper.php
@@ -82,6 +82,9 @@ class ReferenceHelper
      */
     public static function cellSort($a, $b)
     {
+        $ac = $bc = '';
+        $ar = $br = 0;
+
         sscanf($a, '%[A-Z]%d', $ac, $ar);
         sscanf($b, '%[A-Z]%d', $bc, $br);
 
@@ -103,6 +106,9 @@ class ReferenceHelper
      */
     public static function cellReverseSort($a, $b)
     {
+        $ac = $bc = '';
+        $ar = $br = 0;
+
         sscanf($a, '%[A-Z]%d', $ac, $ar);
         sscanf($b, '%[A-Z]%d', $bc, $br);
 
@@ -529,6 +535,8 @@ class ReferenceHelper
             if ($pNumCols != 0) {
                 $autoFilterColumns = $autoFilter->getColumns();
                 if (count($autoFilterColumns) > 0) {
+                    $column = '';
+                    $row = 0;
                     sscanf($pBefore, '%[A-Z]%d', $column, $row);
                     $columnIndex = Coordinate::columnIndexFromString($column);
                     list($rangeStart, $rangeEnd) = Coordinate::rangeBoundaries($autoFilterRange);
diff --git a/src/PhpSpreadsheet/Shared/JAMA/Matrix.php b/src/PhpSpreadsheet/Shared/JAMA/Matrix.php
index 20219004..b3d82d46 100644
--- a/src/PhpSpreadsheet/Shared/JAMA/Matrix.php
+++ b/src/PhpSpreadsheet/Shared/JAMA/Matrix.php
@@ -234,7 +234,7 @@ class Matrix
                     $R = new self($m, $n);
                     for ($i = 0; $i < $m; ++$i) {
                         for ($j = 0; $j < $n; ++$j) {
-                            $R->set($i - $i0, $j - $j0, $this->A[$RL[$i]][$CL[$j]]);
+                            $R->set($i, $j, $this->A[$RL[$i]][$CL[$j]]);
                         }
                     }
 
@@ -257,7 +257,7 @@ class Matrix
                     $R = new self($m, $n);
                     for ($i = $i0; $i < $iF; ++$i) {
                         for ($j = 0; $j < $n; ++$j) {
-                            $R->set($i - $i0, $j, $this->A[$RL[$i]][$j]);
+                            $R->set($i - $i0, $j, $this->A[$i][$CL[$j]]);
                         }
                     }
 
@@ -1013,6 +1013,7 @@ class Matrix
                     if ($this->n == $B->m) {
                         $C = new self($this->m, $B->n);
                         for ($j = 0; $j < $B->n; ++$j) {
+                            $Bcolj = [];
                             for ($k = 0; $k < $this->n; ++$k) {
                                 $Bcolj[$k] = $B->A[$k][$j];
                             }
diff --git a/src/PhpSpreadsheet/Shared/JAMA/QRDecomposition.php b/src/PhpSpreadsheet/Shared/JAMA/QRDecomposition.php
index a123f48d..e666d74b 100644
--- a/src/PhpSpreadsheet/Shared/JAMA/QRDecomposition.php
+++ b/src/PhpSpreadsheet/Shared/JAMA/QRDecomposition.php
@@ -125,6 +125,7 @@ class QRDecomposition
      */
     public function getH()
     {
+        $H = [];
         for ($i = 0; $i < $this->m; ++$i) {
             for ($j = 0; $j < $this->n; ++$j) {
                 if ($i >= $j) {
@@ -147,6 +148,7 @@ class QRDecomposition
      */
     public function getR()
     {
+        $R = [];
         for ($i = 0; $i < $this->n; ++$i) {
             for ($j = 0; $j < $this->n; ++$j) {
                 if ($i < $j) {
@@ -171,6 +173,7 @@ class QRDecomposition
      */
     public function getQ()
     {
+        $Q = [];
         for ($k = $this->n - 1; $k >= 0; --$k) {
             for ($i = 0; $i < $this->m; ++$i) {
                 $Q[$i][$k] = 0.0;
diff --git a/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php b/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php
index 83c9200f..afcf5f47 100644
--- a/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php
+++ b/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php
@@ -126,7 +126,7 @@ class PolynomialBestFit extends BestFit
         // calculate sums
         $x_sum = array_sum($xValues);
         $y_sum = array_sum($yValues);
-        $xx_sum = $xy_sum = 0;
+        $xx_sum = $xy_sum = $yy_sum = 0;
         for ($i = 0; $i < $this->valueCount; ++$i) {
             $xy_sum += $xValues[$i] * $yValues[$i];
             $xx_sum += $xValues[$i] * $xValues[$i];
@@ -140,6 +140,8 @@ class PolynomialBestFit extends BestFit
          *    a series of x-y data points using least squares.
          *
          */
+        $A = [];
+        $B = [];
         for ($i = 0; $i < $this->valueCount; ++$i) {
             for ($j = 0; $j <= $order; ++$j) {
                 $A[$i][$j] = pow($xValues[$i], $j);
diff --git a/src/PhpSpreadsheet/Worksheet/AutoFilter.php b/src/PhpSpreadsheet/Worksheet/AutoFilter.php
index 333aa1b8..494948a7 100644
--- a/src/PhpSpreadsheet/Worksheet/AutoFilter.php
+++ b/src/PhpSpreadsheet/Worksheet/AutoFilter.php
@@ -367,6 +367,8 @@ class AutoFilter
         }
         $returnVal = ($join == AutoFilter\Column::AUTOFILTER_COLUMN_JOIN_AND);
         foreach ($dataSet as $rule) {
+            $retVal = false;
+
             if (is_numeric($rule['value'])) {
                 //    Numeric values are tested using the appropriate operator
                 switch ($rule['operator']) {
@@ -747,6 +749,8 @@ class AutoFilter
                         } else {
                             //    Date based
                             if ($dynamicRuleType[0] == 'M' || $dynamicRuleType[0] == 'Q') {
+                                $periodType = '';
+                                $period = 0;
                                 //    Month or Quarter
                                 sscanf($dynamicRuleType, '%[A-Z]%d', $periodType, $period);
                                 if ($periodType == 'M') {