> For the complete documentation index, see [llms.txt](https://alpaca4d.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alpaca4d.gitbook.io/docs/basics/analysis/run-analysis.md).

# Run Analysis

Writes the model out as an OpenSees `.tcl` deck, launches the solver, and hands back the model with the results attached.

## 🔧 Grasshopper component

`Run Analysis (Alpaca4d)` — **Alpaca4d ▸ 07\_Analysis**

### Inputs

| Name        | Nick          | Type     | Default | Description                                                           |
| ----------- | ------------- | -------- | ------- | --------------------------------------------------------------------- |
| AlpacaModel | `AlpacaModel` | Model    | —       | The assembled model, from [Assemble](/docs/basics/assemble.md).       |
| Settings    | `Settings`    | Settings | —       | From [Analysis Settings](/docs/basics/analysis/analysis-settings.md). |

### Outputs

| Name        | Nick          | Type  | Description                                                                                                                                                                           |
| ----------- | ------------- | ----- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| log         | `log`         | Text  | Everything OpenSees printed — the console output and any error stream. **Read this first when something goes wrong.**                                                                 |
| AlpacaModel | `AlpacaModel` | Model | The same model, now carrying results. Feed it to the [Results](/docs/basics/results.md) and [Visualisation](/docs/basics/visualisation.md) components. `null` if the analysis failed. |

## 💡 Where the files go

The deck and the results are written **next to the Grasshopper file**:

| File              | Contents                  |
| ----------------- | ------------------------- |
| `AlpacaModel.tcl` | The input deck.           |
| `recorder.mpco`   | The MPCO result database. |

If the Grasshopper document has never been saved, Run Analysis falls back to the current working directory. Save the file first — it makes the output findable, and it is required by [Natural Vibration](/docs/basics/analysis/natural-vibration.md).

The recorder that is attached depends on the analysis type: a static recorder for `Static`, a transient one for `Transient`.

## 💡 Errors and how they surface

| What you see                                             | What happened                                                                                                                                                                                                                                        |
| -------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| *"OpenSees executable path is not configured"*           | Set it — **Alpaca4d ▸ Settings ▸ Set OpenSees Executable…**. See [Setup](/docs/setup.md).                                                                                                                                                            |
| *"Analysis Failed: OpenSees exited with an error"*       | The deck itself failed — a bad command, an undefined material. The **log** names the line.                                                                                                                                                           |
| *"Analysis Failed: OpenSees 'analyze' did not converge"* | The deck was valid but the solution did not converge. Loosen the [Test](/docs/basics/analysis/test.md) tolerance, raise its iteration count, take smaller steps in [Analysis Step](/docs/basics/analysis/analysis-step.md), or change the algorithm. |
| *"Warning! Double check the log!"*                       | OpenSees printed a warning and carried on. The results exist but deserve a look.                                                                                                                                                                     |

On any failure the `AlpacaModel` output is `null`, so the downstream result components go quiet rather than showing stale numbers.

## 📈 When to use it

**Use it when** you want a static or transient solution.

**Do not use it when** you want modes and periods → [Natural Vibration](/docs/basics/analysis/natural-vibration.md) sets up its own eigenvalue run and needs no settings.

## 🔗 Relation to OpenSees

The component assembles and runs a complete deck: the model, then the recorder, then the analysis block from [Analysis Settings](/docs/basics/analysis/analysis-settings.md), then `wipe`. To see exactly what was sent, use [Serialize](/docs/basics/utility/serialize.md), or open the `AlpacaModel.tcl` it leaves behind.