# `ZenQuant.Fisher`
[🔗](https://github.com/ZenHive/zen_quant/blob/v0.8.1/lib/zen_quant/fisher.ex#L1)

Fisher Transform oscillator for chronologically ordered price series.

The defaults reproduce Figure 5 of John F. Ehlers, "Using The Fisher
Transform," *Technical Analysis of Stocks & Commodities* 20:11 (November
2002), pp. 40–42: a 10-bar lookback, value EMA alpha of 0.33 (and therefore
prior-value weight 0.67), prior-Fisher weight of 0.5, and bounds of ±0.999.
The article uses median prices `(high + low) / 2`; callers can supply that
series or any other numeric price series.

## API Functions
| Function | Arity | Description | Param Kinds |
| --- | --- | --- | --- |
| `transform` | 2 | Calculate the Fisher Transform and its one-bar-delayed trigger line. | `prices: value` |

# `point`

```elixir
@type point() :: {float(), float()}
```

A Fisher value and its one-bar-delayed trigger value

# `transform`

```elixir
@spec transform(
  [number()],
  keyword()
) :: [point()]
```

Calculate the Fisher Transform and its one-bar-delayed trigger line.

## Parameters

  * `prices` - Numeric prices in chronological order (oldest first) (value)

## Options

  * `lookback` - Rolling normalization window (default: `10`)
  * `value_alpha` - Weight on the current normalized price; the prior-value weight is 1 - alpha (default: `0.33`)
  * `fisher_smoothing` - Weight on the previous Fisher output (default: `0.5`)

## Returns

Chronological \{fisher, trigger\} pairs, or an empty list when fewer prices than the lookback (`list`)

### Example

```elixir
[{0.3428, 0.0}, {0.0621, 0.3428}]
```

```elixir
# descripex:contract
%{
  opts: %{
    lookback: %{
      default: 10,
      type: :integer,
      description: "Rolling normalization window"
    },
    value_alpha: %{
      default: 0.33,
      type: :float,
      description: "Weight on the current normalized price; the prior-value weight is 1 - alpha"
    },
    fisher_smoothing: %{
      default: 0.5,
      type: :float,
      description: "Weight on the previous Fisher output"
    }
  },
  params: %{
    prices: %{
      description: "Numeric prices in chronological order (oldest first)",
      kind: :value
    }
  },
  returns: %{
    type: :list,
    description: "Chronological {fisher, trigger} pairs, or an empty list when fewer prices than the lookback"
  },
  returns_example: [{0.3428, 0.0}, {0.0621, 0.3428}]
}
```

---

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