Creating formulas in Xlio is very similar as in Excel.

var workbook = new Workbook();
var sheet = workbook.Sheets.AddSheet("Sheet1");

sheet["A1"].Value = "Fibonacci Numbers";
sheet["A2"].Value = 1;
sheet["A3"].Value = 1;
for (var r = 3; r < 100; r++)
    sheet[r, 0].Formula = String.Format("={0}+{1}", Cell.Format(r - 1, 0), Cell.Format(r - 2, 0));

//instead of setting formula for each cell it is easier to apply shared formula to a cell range

sheet["B2"].Value = 1;
sheet["B3"].Value = 1;
sheet["B4", "B100"].SetFormula("=B2+B3");

sheet["D1"].Value = "Roots";

var roots = sheet["D2", "F100"];
roots.GetColumns(1, 3).SetStyle(new CellStyle { Format = "0.000" });

foreach (var cdp in roots.GetColumn(0))
    cdp.Data.Value = cdp.Cell.Row + 1;


Composing Formulas

Because formulas work with string cell references (e.g. A3), Cell.Format and Range.Formatfunctions are very useful for composing formula strings.

Circular References

It's easy to mix up row and column numbers and create formulas which contain circular references. Luckily Excel will detect such case and inform the user about it.