<SharePointPermissionAttribute(SecurityAction.InheritanceDemand, ObjectModel:=True)> _
<SharePointPermissionAttribute(SecurityAction.LinkDemand, ObjectModel:=True)> _
Public Class SPFieldCalculated
    Inherits SPField

Dim instance As SPFieldCalculated

[SharePointPermissionAttribute(SecurityAction.InheritanceDemand, ObjectModel=true)] 
[SharePointPermissionAttribute(SecurityAction.LinkDemand, ObjectModel=true)] 
public class SPFieldCalculated : SPField

Dim webSite As SPWeb = SPContext.Current.Site.AllWebs("MyWebSite")
Try
    Dim list As SPList = webSite.Lists("MyList")
    Dim fields As SPFieldCollection = list.Fields

    Dim newFieldName As String = fields.Add("MyNewColumn", SPFieldType.Calculated, False)
    Dim newField As SPFieldCalculated = CType(fields(newFieldName), SPFieldCalculated)
    newField.Formula = "=[MyColumn1]<[MyColumn2]"
    newField.Update()

    Dim view As SPView = list.Views("MyView")
    Dim viewFields As SPViewFieldCollection = view.ViewFields
    viewFields.Add(newFieldName)
    view.Update()
Finally
    webSite.Dispose()
End Try

using (SPWeb oWebsite = SPContext.Current.Site.AllWebs["Website_Name"])
{
    SPList oList = oWebsite.Lists["MyList"];
    SPFieldCollection collFields = oList.Fields;

    string strNewFieldName = collFields.Add("MyNewColumn", 
        SPFieldType.Calculated, false);
    SPFieldCalculated strNewField =       
        (SPFieldCalculated)collFields[strNewFieldName];
    strNewField.Formula = "=[Column1]<[Column2]";
    strNewField.Update();

    SPView oView = oList.Views["MyView"];
    SPViewFieldCollection collViewFields = oView.ViewFields;
    collViewFields.Add(strNewFieldName);
    oView.Update();
}