u/qwqq123

I’ve been thinking about adding execution portability to the robustness checks I use before trusting an algo, but I’m not convinced it’s actually a fair requirement.

Basic problem is pretty simple

I can keep the signal logic, sizing and exits completely unchanged and still get a very different system once I change the assumptions around execution.

So instead of only stress testing parameters and market regimes, I’m considering testing the execution layer separately.

Something like this

Baseline

• normal spread assumption
• normal commission model
• current slippage assumption
• normal fill probability

Stress test A	spread 25% worse
Stress test B	spread 50% worse
Stress test C	normal spread	1 tick adverse slippage on entry and exit
Stress test D	spread 25% worse	some adverse slippage	small fill delay	a percentage of limit orders left unfilled

I’d then compare more than just final P/L

The metrics I’m thinking about are

• expectancy per trade
• profit factor
• Sharpe
• max drawdown
• fill rate
• percentage of gross edge lost to execution
• trade count after missed fills

Numbers above are just hypothetical stress parameters. I’m more interested in the framework than those exact thresholds.

Here’s where I’m getting stuck.

Say a strategy has a PF around 1.30 under the baseline execution model. A modest increase in spread brings it close to 1.10. Add a little adverse slippage and it drops below breakeven.

There are two completely different ways I can read that.

The first is that the strategy was fragile from the start. If a small change in trading costs wipes out the edge, I probably shouldn’t trust the backtest much. Second is that this is asking the strategy to survive something it was never designed for. A short-horizon system can have a real edge that only exists with a specific fee structure, spread, order type or execution venue. In that case the execution environment isn’t noise around the strategy. It’s part of the strategy.

That second case is what makes broker portability questionable to me as a robustness test. I wouldn’t expect a market-making system to keep the same economics after changing the fee structure. I also wouldn’t expect a tight scalper to behave the same after doubling its spread assumptions. At some point I’m no longer stress testing the same business logic. I’m changing the conditions that created the edge in the first place.

But giving the execution model zero robustness testing seems just as bad.
Backtest that only works at one exact spread and one exact slippage assumption feels way too brittle for live trading.

So I’m leaning toward measuring an execution degradation curve instead of using a simple pass or fail rule.

Basically I want to know how quickly the edge decays as execution gets worse.

A gradual decay seems a lot healthier to me than a strategy that falls off a cliff after one extra tick.

What I don’t know is where that becomes unacceptable.

For people running systems live, how do you handle this?

Do you expect an algo to remain profitable across moderately worse execution assumptions, or are you fine with an edge being tightly tied to one broker, venue or fee structure as long as those conditions are stable?

And if you stress test execution, what do you actually perturb: spread, commissions, latency, fill probability, slippage distributions, or all of them together?

I’m 35 and live in Andalusia, Spain. I’m getting serious about opening my own hair salon and the part I’m stuck on right now is how to finance it without getting in over my head before the doors even open.
Plan is pretty simple one location, a amall team or possibly just myself at the beginning, and enough equipment to operate properly without going crazy on the interior right out of gate.

Startup money would mainly go toward:

• lease deposit and the first months of rent
• basic renovation
• salon chairs and mirrors
• wash stations
• dryers and professional tools
• first stock of hair products
• permits and insurance
• signage and basic marketing
• working capital the first few months

I’m still building the final budget because I want to separate what is actually needed on day one from the stuff that would just be nice to have.

1. Financing options I’m looking at the traditional route would be a business loan through a bank. So far I’ve been looking at Unicaja, MicroBank and BBVA. I’m also checking whether an ICO-backed loan could make sense depending on the final amount and requirements. Unicaja caught my attention because they have financing specifically aimed at starting a first business. MicroBank also looks relevant because of its focus on entrepreneurs and small businesses. Outside the normal banking route I’ve also looked at Maclear as a P2B financing option. I’m still trying to understand how crowd lending actually works from the borrower side and whether the total cost, documentation, collateral requirements and funding timeline would make sense for a brand-new salon. I’m not assuming any of these options is automatically better. I want to compare the actual offer I could get from each one.
2. Part that worries me A monthly payment can look totally fine on paper if the salon is busy. The problem is the first 6 to 12 months. There is no guarantee that enough regular clients will show up immediately, and rent, utilities, products, insurance and the loan payment will still be there every month. That makes me wonder whether taking a bigger loan to open exactly the way I want is a bad move compared with starting lean and upgrading the salon once the customer base is there.
3. Things I’m trying to work out before borrowing How much of the startup cost should realistically come from my own savings? How many months of operating expenses should stay untouched as a cash reserve? Would it make more sense to finance equipment separately instead of putting everything into one loan? For a service business like a salon, what debt payment would you consider too high compared with conservative monthly revenue? And for people who opened a salon, barbershop, beauty studio or another local service business, what expense ended up being way higher than expected? I’m especially interested in hearing from anyone who has dealt with Spanish banks, microcredit, ICO financing or other small-business lending in Europe. The goal is not to find the biggest amount someone will lend me. I’m trying to figure out which structure gives the business enough breathing room to survive a slow start without burning through cash or becoming dependent on debt from day one.