Fatal error: Uncaught Error: Class 'Matrix' not found in /opt/lampp/htdocs/dhtmlxSuite_v5.1/codebase/grid-excel-php/lib/PHPExcel.original/Shared/JAMA/examples/LagrangeInterpolation2.php:40 Stack trace: #0 /opt/lampp/htdocs/dhtmlxSuite_v5.1/codebase/grid-excel-php/lib/PHPExcel.original/Shared/JAMA/examples/LagrangeInterpolation2.php(55): LagrangeInterpolation->findPolynomialFactors(Array, Array) #1 {main} thrown in /opt/lampp/htdocs/dhtmlxSuite_v5.1/codebase/grid-excel-php/lib/PHPExcel.original/Shared/JAMA/examples/LagrangeInterpolation2.php on line 40