# `BB.Error.Estimator.MissingCovariance`
[🔗](https://github.com/beam-bots/bb/blob/main/lib/bb/error/estimator/missing_covariance.ex#L5)

An algorithm required a covariance field on an input payload but the
upstream publisher left it `nil`.

Many Kalman-family algorithms cannot proceed without measurement
noise. They may either fall back to a configured default or raise
this error, depending on configuration.

# `t`

```elixir
@type t() :: %BB.Error.Estimator.MissingCovariance{
  __exception__: true,
  bread_crumbs: term(),
  class: term(),
  estimator: atom(),
  field: atom(),
  path: term(),
  splode: term(),
  stacktrace: term(),
  vars: term()
}
```

# `exception`

```elixir
@spec exception(opts :: Keyword.t()) :: %BB.Error.Estimator.MissingCovariance{
  __exception__: true,
  bread_crumbs: term(),
  class: term(),
  estimator: term(),
  field: term(),
  path: term(),
  splode: term(),
  stacktrace: term(),
  vars: term()
}
```

Create an `Elixir.BB.Error.Estimator.MissingCovariance` without raising it.

## Keys

- :estimator
- :field

---

*Consult [api-reference.md](api-reference.md) for complete listing*