If you sell a security short, you must have sufficient equity in your account to cover any fees associated with borrowing the security. If you borrow the security through us, we will borrow the security on your behalf and your account must have sufficient collateral to cover the margin requirements of the short sale. To cover administrative fees and stock borrowing fees, we must post 102% of the value of the security borrowed as collateral with the lender. In instances in which the security shorted is hard to borrow, borrowing fees charged by the lender may be so high (greater than the interest earned) that the short seller must pay additional interest for the privilege of borrowing a security. Customers may view the indicative short stock interest rates for a specific stock through the Short Stock (SLB) Availability tool located in the Tools section of their Account Management page. For more information concerning shorting stocks and associated fees, visit our Stock Shorting page.
In particular I've made the interface for beginning a new backtest a lot simpler by encapsulating a lot of the "boilerplate" code into a new Backtest class. I've also modified the system to be fully workable with multiple currency pairs. In this article I'll describe the new interface and show the usual Moving Average Crossover example on both GBP/USD and EUR/USD.
Imagine that you have $10,000 on your account account, and you have a losing position with a margin evaluated at $1,000. If your position goes against you, and it goes to a $9,000 loss, the equity will be $1,000 (i.e $10,000 - $9,000), which equals the margin. Thus, the margin level will be 100%. Again, if the margin level reaches the rate of 100%, you can't take any new positions, unless the market suddenly turns around and your equity level turns out to be greater than the margin.
Whether you have assets in a securities account or in a futures account, your assets are protected by U.S. federal regulations governing how brokers must protect your property and funds. In the securities account, your assets are protected by SEC and SIPC rules. In the futures account, your assets are protected by CFTC rules requiring segregation of customer funds. You are also protected by our strong financial position and our conservative risk management philosophy. See our Strength & Security page.

Imagine that you have $10,000 on your account account, and you have a losing position with a margin evaluated at $1,000. If your position goes against you, and it goes to a $9,000 loss, the equity will be $1,000 (i.e $10,000 - $9,000), which equals the margin. Thus, the margin level will be 100%. Again, if the margin level reaches the rate of 100%, you can't take any new positions, unless the market suddenly turns around and your equity level turns out to be greater than the margin.
Now that we have discussed the longer term plan I want to present some of the changes I have made to the code since diary entry #2. In particular, I want to describe how I modified the code to handle the Decimal data-type instead of using floating point storage. This is an extremely important change as floating point representations are a substantial source of long-term error in portfolio and order management systems.

The market values/prices used to compute the equity or margin requirement in an Interactive account may differ from the price disseminated by exchanges or other market data sources, and may represent Interactive's valuation of the product. Among other things, Interactive may calculate its own index values, Exchange Traded Fund values or derivatives values, and Interactive may value securities or futures or other investment products based on bid price, offer price, last sale price, midpoint or using some other method. Interactive may use a valuation methodology that is more conservative than the marketplace as a whole.

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