Running Product in DAX: Calculating Portfolio Returns

Recently a friend of mine asked me how to calculate investment rates of return in PowerPivot. In order to do this, one must be able to run over a list of values using a multiplication. Currently, DAX does not have a ProductX or MultiplyX function to evaluate an expression in a specified row context followed by a final pass to multiply all computed values. I dealt with this issue in MDX years ago when attempting to do the same. Although in that case I used the Multiply() .Net stored procedure to achieve the goal within the expression, I still recall seeing how Mosha pointed out a way to mimic a running multiplication using the following formula: