Pentaho formula: Begginning of the week date (last monday)
=IF(DAY(TODAY()) - WEEKDAY(TODAY()) -2 > 0;DATE(YEAR(TODAY());MONTH(TODAY());DAY(TODAY())- WEEKDAY(TODAY()) + 3);IF (MONTH(TODAY()) > 1 ; DATE( YEAR(TODAY()); MONTH(TODAY()) -1 ; DAY(MONTHEND(DATE(YEAR(TODAY());MONTH(TODAY())-1;1)))-WEEKDAY(MONTHEND(DATE(YEAR(TODAY());MONTH(TODAY())-1;1) )) +3);DATE( YEAR(TODAY())-1; 12 ; DAY(MONTHEND(DATE(YEAR(TODAY() -1 );12;1))) -WEEKDAY( MONTHEND(DATE(YEAR(TODAY()-1);12;1) )) +3)))