Add documentation for scipy_cobyqa

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: timmens

docs/source/algorithms.md

@@ -313,6 +313,35 @@ automatically installed when you install optimagic.
 
 ```
 
+```{eval-rst}
+.. dropdown::  scipy_cobyqa
+
+    **How to use this algorithm:**
+
+    .. code-block::
+
+        import optimagic as om
+        om.minimize(
+          ...,
+          algorithm=om.algos.scipy_cobyqa(stopping_maxfun=1_000, ...)
+        )
+
+    or
+
+    .. code-block::
+
+        om.minimize(
+          ...,
+          algorithm="scipy_cobyqa",
+          algo_options={"stopping_maxfun": 1_000, ...}
+        )
+
+    **Description and available options:**
+
+    .. autoclass:: optimagic.optimizers.scipy_optimizers.ScipyCOBYQA
+
+```
+
 ```{eval-rst}
 .. dropdown::  scipy_truncated_newton
 

src/optimagic/optimizers/scipy_optimizers.py

@@ -544,24 +544,17 @@ class ScipyCOBYQA(Algorithm):
 
     """
 
-    stopping_maxfun: PositiveInt | None = None
-    """Maximum number of function evaluations.
-
-    Defaults to 500 * n, where n is the number of variables.
-
-    """
-
-    stopping_maxiter: PositiveInt | None = None
-    """Maximum number of iterations.
-
-    Defaults to 1000 * n, where n is the number of variables.
+    stopping_maxfun: PositiveInt = STOPPING_MAXFUN
+    """Maximum number of function evaluations."""
 
-    """
+    stopping_maxiter: PositiveInt = STOPPING_MAXITER
+    """Maximum number of iterations."""
 
     convergence_ftol_abs: NonNegativeFloat | None = None
-    """Tolerance for the objective function value.
+    """Target objective function value.
 
     The algorithm stops when the objective function value is below this threshold.
+    Disabled by default.
 
     """
 
@@ -597,17 +590,15 @@ def _solve_internal_problem(
             radius = self.trustregion_initial_radius
 
         options: dict[str, Any] = {
+            "maxfev": self.stopping_maxfun,
+            "maxiter": self.stopping_maxiter,
             "initial_tr_radius": radius,
             "final_tr_radius": self.trustregion_final_radius,
             "feasibility_tol": self.feasibility_tol,
             "scale": self.scale,
             "disp": self.display,
         }
 
-        if self.stopping_maxfun is not None:
-            options["maxfev"] = self.stopping_maxfun
-        if self.stopping_maxiter is not None:
-            options["maxiter"] = self.stopping_maxiter
         if self.convergence_ftol_abs is not None:
             options["f_target"] = self.convergence_ftol_abs