Working with One-Way Turnover Constraints Using PortfolioCVaR Object

One-way turnover constraints are optional constraints (see One-way Turnover Constraints) that enforce upper bounds on net purchases or net sales. One-way turnover constraints can be set using the PortfolioCVaR object or the setOneWayTurnover function. One-way turnover constraints depend upon an initial or current portfolio, which is assumed to be zero if not set when the turnover constraints are set. One-way turnover constraints have properties BuyTurnover, for the upper bound on net purchases, SellTurnover, for the upper bound on net sales, and InitPort, for the portfolio against which turnover is computed.

Setting One-Way Turnover Constraints Using the PortfolioCVaR Function

The Properties for the one-way turnover constraints are set using the PortfolioCVaR object. Suppose that you have an initial portfolio with 10 assets in a variable x0 and you want to ensure that turnover on purchases is no more than 30% and turnover on sales is no more than 20% of the initial portfolio. To set these turnover constraints:

x0 = [ 0.12; 0.09; 0.08; 0.07; 0.1; 0.1; 0.15; 0.11; 0.08; 0.1 ]; 
p = PortfolioCVaR('BuyTurnover', 0.3, 'SellTurnover', 0.2, 'InitPort', x0);
disp(p.NumAssets);
disp(p.BuyTurnover);
disp(p.SellTurnover);
disp(p.InitPort);  
    10

    0.3000

    0.2000

    0.1200
    0.0900
    0.0800
    0.0700
    0.1000
    0.1000
    0.1500
    0.1100
    0.0800
    0.1000

If the NumAssets or InitPort properties are not set before or when the turnover constraint is set, various rules are applied to assign default values to these properties (see Setting Up an Initial or Current Portfolio).

Setting Turnover Constraints Using the setOneWayTurnover Function

You can also set properties for portfolio turnover using setOneWayTurnover to specify to the upper bounds for turnover on purchases (BuyTurnover) and sales (SellTurnover) and an initial portfolio. Suppose that you have an initial portfolio of 10 assets in a variable x0 and want to ensure that turnover on purchases is no more than 30% and that turnover on sales is no more than 20% of the initial portfolio. Given a PortfolioCVaR object p, use setOneWayTurnover to set the turnover constraints with and without the initial portfolio being set previously:

x0 = [ 0.12; 0.09; 0.08; 0.07; 0.1; 0.1; 0.15; 0.11; 0.08; 0.1 ];
p = PortfolioCVaR('InitPort', x0);
p = setOneWayTurnover(p, 0.3, 0.2);

disp(p.NumAssets);
disp(p.BuyTurnover);
disp(p.SellTurnover);
disp(p.InitPort);
    10

    0.3000

    0.2000

    0.1200
    0.0900
    0.0800
    0.0700
    0.1000
    0.1000
    0.1500
    0.1100
    0.0800
    0.1000
or
x0 = [ 0.12; 0.09; 0.08; 0.07; 0.1; 0.1; 0.15; 0.11; 0.08; 0.1 ];
p = PortfolioCVaR;
p = setOneWayTurnover(p, 0.3, 0.2, x0);
disp(p.NumAssets);
disp(p.BuyTurnover);
disp(p.SellTurnover);
disp(p.InitPort);
    10

    0.3000

    0.2000

    0.1200
    0.0900
    0.0800
    0.0700
    0.1000
    0.1000
    0.1500
    0.1100
    0.0800
    0.1000

setOneWayTurnover implements scalar expansion on the argument for the initial portfolio. If the NumAssets property is already set in the PortfolioCVaR object, a scalar argument for InitPort expands to have the same value across all dimensions. In addition, setOneWayTurnover lets you specify NumAssets as an optional argument. To remove one-way turnover from your PortfolioCVaR object, use thePortfolioCVaR object or setOneWayTurnover with empty inputs for the properties to be cleared.

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