New tutorial on learning mascons, doc additions.

doc/api_model.rst

@@ -14,3 +14,4 @@ Functions
    cart2geo
    nrlmsise00_tn
    jb08_tn
+   fixed_centres

doc/examples_astro.rst

@@ -43,3 +43,4 @@ Celestial mechanics and astrodynamics
   notebooks/tides_spokes
   notebooks/lagrangian_propagator
   notebooks/gg_stab
+  notebooks/learning_mascons

heyoka/_test_model.py

@@ -101,6 +101,7 @@ def test_rotating(self):
 
     def test_fixed_centres(self):
         from . import model, make_vars, expression as ex, sqrt
+        from numpy import single
 
         x, y, z, vx, vy, vz = make_vars("x", "y", "z", "vx", "vy", "vz")
 
@@ -140,6 +141,15 @@ def test_fixed_centres(self):
             in str(cm.exception)
         )
 
+        # Run also a small test with single-precision values.
+        dyn = model.fixed_centres(
+            Gconst=single(1.5), masses=[single(1.1)], positions=[[1.0, 2.0, 3.0]]
+        )
+
+        self.assertEqual(dyn[0][0], x)
+        self.assertEqual(dyn[0][1], ex("vx"))
+        self.assertTrue("1.10000002" in repr(dyn))
+
     def test_nbody(self):
         from . import model, expression, sqrt, make_vars
 

heyoka/docstrings.cpp

@@ -678,4 +678,31 @@ std::string var_args_all()
 )";
 }
 
+std::string fixed_centres()
+{
+    return R"(fixed_centres(Gconst: expression | str | numpy.single | float | numpy.longdouble = 1., masses: list[expression | str | numpy.single | float | numpy.longdouble] = [], positions: collections.abc.Iterable = numpy.empty((0, 3), dtype=float)) -> list[tuple[expression, expression]]
+
+Produces the expression for the dynamics of a fixed-centres problem.
+
+In the fixed-centres problem, a number of massive particles are fixed in space, which each mass generating
+a Newtonian gravitational field.
+
+Several checks are run on the input arguments:
+
+- *positions* must be convertible into an ``N x 3`` array, with each row containing
+  the position vector of a mass,
+- the number of elements in *masses* must be the same as the number of three-dimensional
+  position vectors in *positions*.
+
+:param Gconst: the gravitational constant.
+:param masses: the list of mass values (one for each particle).
+:param positions: the positions of the particles.
+
+:returns: the dynamics of the Newtonian fixed centres problem.
+
+:raises ValueError: if one or more input arguments are malformed, as explained above.
+
+)";
+}
+
 } // namespace heyoka_py::docstrings

heyoka/docstrings.hpp

@@ -48,6 +48,7 @@ std::string hamiltonian();
 std::string cart2geo();
 std::string nrlmsise00_tn();
 std::string jb08_tn();
+std::string fixed_centres();
 
 // var_ode_sys() and related.
 std::string var_args();

heyoka/expose_models.cpp

@@ -46,6 +46,7 @@
 
 #include "common_utils.hpp"
 #include "custom_casters.hpp"
+#include "docstrings.hpp"
 #include "dtypes.hpp"
 #include "expose_models.hpp"
 
@@ -207,7 +208,7 @@ void expose_models(py::module_ &m)
 
     // A variant containing either an expression or a numerical/string
     // type from which an expression can be constructed.
-    using vex_t = std::variant<hy::expression, std::string, double, long double
+    using vex_t = std::variant<hy::expression, std::string, float, double, long double
 #if defined(HEYOKA_HAVE_REAL128)
                                ,
                                mppp::real128
@@ -276,7 +277,8 @@ void expose_models(py::module_ &m)
             return detail::fixed_centres_impl(hy::model::fixed_centres, Gconst, masses, positions);
         },
         "Gconst"_a.noconvert() = 1., "masses"_a.noconvert() = py::list{},
-        "positions"_a = py::array{py::dtype(get_dtype<double>()), py::array::ShapeContainer{0, 3}});
+        "positions"_a = py::array{py::dtype(get_dtype<double>()), py::array::ShapeContainer{0, 3}},
+        docstrings::fixed_centres().c_str());
     m.def(
         "_model_fixed_centres_energy",
         [](const vex_t &Gconst, const std::vector<vex_t> &masses, const py::iterable &positions) {