I think my algorithm is spending more money than it has.

I think my algorithm is spending more money than it has. I have done a bit of research on it but haven't been able to figure it out in over in hour. It is probably an easy fix for you guys though. Thanks

5
Backtest from to with initial capital
Total Returns
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Sortino
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 Max Drawdown 1 Month 3 Month 6 Month 12 Month
# Backtest ID: 531520ffd6b9f10747fedd9a
This backtest was created using an older version of the backtester. Please re-run this backtest to see results using the latest backtester. Learn more about the recent changes.
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5 responses

I'm just guessing, so it would be nice if someone else could confirm or refute this.

if you insert the following at rows 18/19, you can at least see what is happening to your cash:

def handle_data(context, data):
record(cash=context.portfolio.cash)


As you'll see, the cash balance goes from $100k to -$651k almost immediately.

I added a counter to the loop, and it looks like your subset of the universe is around 180 stocks. When you initially cycle through the portfolio, your cash will not change after you place an order but will only be reduced once the order has been executed, which should be observable at the next bar.

Putting another counter in line 25 of your code in the rsi long loop, I can see that the initial execution was to buy 37 tickers on 2008-01-25. Given that you are buying $20k per ticker, that would be about$740k. Starting cash of $100k -$740k = -$640k, so we are in the ballpark with the -$651k observed earlier.

I'm not sure what mechanisms Quantopian has in place to fail executions once cash has been depleted.

this seems similar to my question about selling short: https://www.quantopian.com/posts/how-to-sell-short

you should consider using order_target_percent() instead. i changed my algo to use that (instead of an actual cash/stock amount) and everything's now working good.

I would like to see an answer from the Q staff about the handling of context.portfolio.cash.
I see two problems:
1) When an order long is sent, the "available cash" should be immediately decreased (yes, maybe a new field is required...). This would make thing much more realistic and comparable to what happens when working with real money.
2) For the same reason (good simulation of real operation), when a short order is sent the available cash should be immediately decreased by the margin amount (typically 50% of the value sold).
In my opinion these tasks, being always the same, should be handled by the platform, not by the algorithms.

Hi Leopoldo,

1. That's an interesting idea - I'd like to understand why you're looking for that. Currently if you have a field in you algo called "available_cash" or "get_open_orders", checking either of these fields is the same amount of work. In your algo, the available cash is decreased once the orders are filled to mimic real-world conditions. We created this behavior because you cannot know the price until the order is filled. We have other convenient methods for cash management, including order_target_value() and order_target_percent() as Jason mentioned.

2. A margin model is a great idea! And we've gotten a lot of requests for it. It's on our wish list and we hope to implement it in the future. Until there is a convenient built-in function, try using this code shared by David: https://www.quantopian.com/posts/margin-requirements

Cheers,
Alisa

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Thanks guys! Colin, thanks for examining my algorithm for me. I wasn't aware that the portfolio.cash is only updated daily/minutely. Jason, I implemented what you recommended I set the max position I could own in any stock equal to 100/180 %. I don’t think it is working perfectly yet, but I’ll work on it.