numpy type missmatch during beangrow-returns if price difference too big

[tuhriel]

I have a portfolio for which the creation of the reports fails with the following error:

Traceback (most recent call last):
  File "/home/stefan/gitrepos/ledger_test/.venv/bin/beangrow-returns", line 10, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/stefan/gitrepos/ledger_test/.venv/lib/python3.12/site-packages/beangrow/compute_returns.py", line 86, in main
    pricer = reports.generate_reports(account_data_map, config,
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/stefan/gitrepos/ledger_test/.venv/lib/python3.12/site-packages/beangrow/reports.py", line 641, in generate_reports
    func()
  File "/home/stefan/gitrepos/ledger_test/.venv/lib/python3.12/site-packages/beangrow/reports.py", line 242, in write_returns_html
    plots = plot_flows(
            ^^^^^^^^^^^
  File "/home/stefan/gitrepos/ledger_test/.venv/lib/python3.12/site-packages/beangrow/reports.py", line 492, in plot_flows
    gamounts[-remaining_days:] += gflow
numpy._core._exceptions._UFuncOutputCastingError: Cannot cast ufunc 'add' output from dtype('complex128') to dtype('float64') with casting rule 'same_kind'

I was able to identify which asset is creating the issue and have pulled all the entries to this specific asset. I'm at a loss what exactly leads to this issue. I tried to find the issue by:

• changing the source of the price information between coinbase and yahoo
• modifying the prices to have less decimals
• modifying the amount of bought assets to have less decimals
• removing the inferred_tolerance_default value for EUR

it still kept throwing the error and stopping the finalization of the report.

while writing this issue, I got the idea that it might be missing some prices, so I added some prices....nothing..still an error

I removed the most current price: 2025-12-16 price SOL 107.825 EUR

I did some additional testing with the dates and prices and voila I found it:
2025-12-14 price SOL 111.517886352539060000 EUR --> Error
2025-12-14 price SOL 111.557886352539060000 EUR --> OK

somehow the calculation fails, if the current price falls too low (or maybe the difference grows too large). That's where my python debugging skills end, as I can't figure out which two variables it want's to add up.

beancount file:

option "operating_currency" "CHF"

option "booking_method" "FIFO"
option "inferred_tolerance_default" "USD:0.00001"
option "inferred_tolerance_default" "EUR:0.0001"
option "inferred_tolerance_default" "SEK:0.00001"

plugin "beancount.plugins.implicit_prices"


2025-03-18 commodity SOL
	price: "EUR:coinbase/SOL-EUR"
2025-03-18 open Assets:CH:Swissquote:SOL
2025-03-18 open Income:CH:Swissquote:PnL:SOL


1900-01-01 commodity EUR
	price: "CHF:ratesapi/EUR-CHF"
    

2025-10-23 * "Kauf 1.21 SOL"
    Assets:CH:Swissquote:SOL                    1.21350534 SOL  { 163.16 EUR }
    Assets:CH:Swissquote:Cash:EUR            - 199.98 EUR
    Expenses:CH:Swissquote:Kommission            1.98 EUR



2025-11-18 price SOL                121.51249694824219 EUR
2025-12-16 price SOL                    107.825 EUR

beangrow config:

investments{
  investment {
    currency: "SOL"
    asset_account: "Assets:CH:Swissquote:SOL"
    cash_accounts: "Assets:CH:Swissquote:Cash:EUR"
  }
}
groups{
  group {
    name: "currency.SOL"
    investment: "Assets:CH:Swissquote:SOL"
  }
}

this is the output (up until it is stopped by the error above) if run with --verbose:

INFO    : Reading ledger: sol.beancount
DEBUG   : Processing account: Assets:CH:Swissquote:SOL
INFO    : Writing details file: ./sol/investments/Assets_CH_Swissquote_SOL.org
INFO    : Writing returns dir for currency.SOL: sol/groups/currency.SOL
DEBUG   : Inside Dietz. From None to 2025-12-16
DEBUG   : Setting start date to 2025-10-23
DEBUG   : Start date: 2025-10-23
DEBUG   : End date: 2025-12-16
DEBUG   : PnL: 130.8462132855 + 0.0 - 199.98 = -69.13378671449999
DEBUG   : Average capital: -0.0 + 203.68333333333334 = 203.68333333333334
DEBUG   : Dietz return: -0.33941798566974873
DEBUG   : Inside Dietz. From None to 2025-12-16
DEBUG   : Setting start date to 2025-10-23
DEBUG   : Start date: 2025-10-23
DEBUG   : End date: 2025-12-16
DEBUG   : PnL: 130.8462132855 + 0.0 - 199.98 = -69.13378671449999
DEBUG   : Average capital: -0.0 + 203.68333333333334 = 203.68333333333334
DEBUG   : Dietz return: -0.33941798566974873
DEBUG   : Loaded backend agg version v2.2.