Document model options in FEAScriptWorker

setModelConfig and solve take the same options as FEAScriptModel.
Explain that coefficient functions are sent as source code, so they must
not use outer variables, and that a Content Security Policy must allow
'unsafe-eval'. Remove the limitations this fixes.

Author: nikoscham

docs/api/web-worker.md

@@ -53,25 +53,54 @@ model.terminate();
 
 | Method                                         | Returns            | Description                                                      |
 | ---------------------------------------------- | ------------------ | ---------------------------------------------------------------- |
-| `setModelConfig(modelConfig)`                  | `Promise<boolean>` | Selects the model (name only, see the note below)                |
+| `setModelConfig(modelConfig, options)`         | `Promise<boolean>` | Selects the model and its options, as `FEAScriptModel`           |
 | `setMeshConfig(meshConfig)`                    | `Promise<boolean>` | Sets the mesh, as `FEAScriptModel.setMeshConfig`                 |
 | `addBoundaryCondition(boundaryKey, condition)` | `Promise<boolean>` | Adds a boundary condition                                        |
 | `setSolverMethod(solverMethod)`                | `Promise<boolean>` | Selects the solver method                                        |
-| `solve()`                                      | `Promise<object>`  | Solves the model in the worker                                   |
+| `solve(options)`                               | `Promise<object>`  | Solves the model in the worker (`maxIterations`, `tolerance`)    |
 | `getModelInfo()`                               | `Promise<object>`  | `{ solverConfig, meshConfig, boundaryConditions, solverMethod }` |
 | `ping()`                                       | `Promise<boolean>` | Resolves to `true` when the worker is ready                      |
 | `terminate()`                                  | –                  | Stops the worker                                                 |
 
 `solve()` resolves to `{ solutionVector, nodesCoordinates, solverConfig, meshDimension }`. The object returned by
 `getModelInfo()` can be passed as the `model` argument of the [plotting functions](./visualization.md).
 
+## Model options
+
+`setModelConfig` and `solve` take the same options as in `FEAScriptModel`, including `coefficientFunctions`,
+`nonlinear`, `maxIterations` and `tolerance`:
+
+```javascript
+await model.setModelConfig("generalFormPDEScript", {
+  coefficientFunctions: {
+    A: (x) => 1, // Diffusion coefficient
+    B: (x) => -10, // Advection coefficient
+    C: (x) => 0, // Reaction coefficient
+    D: (x) => 10 * Math.exp(-200 * Math.pow(x - 0.5, 2)), // Source term
+  },
+});
+```
+
+Functions cannot be sent to a web worker, so `FEAScriptWorker` sends each coefficient function as its source code
+and rebuilds it in the worker. A rebuilt function does not have access to the variables around it, so write the
+values into the function:
+
+```javascript
+const Da = 0.5;
+
+// Does not work in the worker: Da is not defined there
+D: (x, u) => Da * u ** 2,
+
+// Works in the worker
+D: (x, u) => 0.5 * u ** 2,
+```
+
+Use functions defined in your own code: built-in functions such as `Math.sin` must be wrapped, e.g.
+`(x) => Math.sin(x)`. Rebuilding the functions requires `eval`, so a page with a
+[Content Security Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) must allow `'unsafe-eval'`.
+
 ## Limitations
 
-- `setModelConfig` takes only the model name: model options such as `coefficientFunctions`, `nonlinear`,
-  `maxIterations` and `tolerance` cannot be passed to the worker (functions cannot be sent to a web worker). Models
-  that need coefficient functions (the general form PDE and the Euler–Bernoulli beam) can therefore not run in
-  the worker yet, and heat conduction runs with the default coefficients ($k = 1$, $Q = 0$).
-- `solve()` takes no options, so the solvers run with their default `maxIterations` and `tolerance`.
 - `solveAsync` and the `"jacobi-gpu"` method are not available through the worker.
 
 ## Examples