FormulaRecord fr = new FormulaRecord();
fr.setRow(rownum);
fr.setColumn((short)colnum);
FormulaRecordAggregate agg = new FormulaRecordAggregate(fr, null, SharedValueManager.createEmpty());
Ptg[] ptgsForCell = {new ExpPtg(rownum, colnum)};
agg.setParsedExpression(ptgsForCell);
String formula = "SUM(A1:A3*B1:B3)";
Ptg[] ptgs = HSSFFormulaParser.parse(formula, null, FormulaType.ARRAY, 0);
agg.setArrayFormula(new CellRangeAddress(rownum, rownum, colnum, colnum), ptgs);