Add make_kron binding for the native kron atom

sparsediffpy/_bindings/atoms/kron.h

@@ -0,0 +1,54 @@
+#ifndef ATOM_KRON_H
+#define ATOM_KRON_H
+
+#include "common.h"
+
+/* Kronecker product Z = kron(A, B). Exactly one operand is variable-free and is
+ * passed as the parameter capsule (wrap constants with make_parameter and
+ * param_id=-1 / PARAM_FIXED); the other carries the variables and is passed as
+ * the child capsule.
+ *
+ * Python signature:
+ *   make_kron(param_capsule, child_capsule, const_is_left, p, q, r, s)
+ * - const_is_left: 1 -> A=param, B=child; 0 -> A=child, B=param.
+ * - (p, q): A's dims; (r, s): B's dims. */
+static PyObject *py_make_kron(PyObject *self, PyObject *args)
+{
+    PyObject *param_capsule;
+    PyObject *child_capsule;
+    int const_is_left, p, q, r, s;
+
+    if (!PyArg_ParseTuple(args, "OOiiiii", &param_capsule, &child_capsule,
+                          &const_is_left, &p, &q, &r, &s))
+    {
+        return NULL;
+    }
+
+    expr *param_node =
+        (expr *) PyCapsule_GetPointer(param_capsule, EXPR_CAPSULE_NAME);
+    if (!param_node)
+    {
+        PyErr_SetString(PyExc_ValueError, "invalid parameter capsule");
+        return NULL;
+    }
+
+    expr *child =
+        (expr *) PyCapsule_GetPointer(child_capsule, EXPR_CAPSULE_NAME);
+    if (!child)
+    {
+        PyErr_SetString(PyExc_ValueError, "invalid child capsule");
+        return NULL;
+    }
+
+    expr *node = new_kron(param_node, child, const_is_left, p, q, r, s);
+    if (!node)
+    {
+        PyErr_SetString(PyExc_RuntimeError, "failed to create kron node");
+        return NULL;
+    }
+
+    expr_retain(node); /* Capsule owns a reference */
+    return PyCapsule_New(node, EXPR_CAPSULE_NAME, expr_capsule_destructor);
+}
+
+#endif /* ATOM_KRON_H */

sparsediffpy/_bindings/bindings.c

@@ -16,6 +16,7 @@
 #include "atoms/getters.h"
 #include "atoms/hstack.h"
 #include "atoms/index.h"
+#include "atoms/kron.h"
 #include "atoms/left_matmul.h"
 #include "atoms/log.h"
 #include "atoms/logistic.h"
@@ -94,6 +95,8 @@ static PyMethodDef DNLPMethods[] = {
      "Create elementwise multiply node"},
     {"make_convolve", py_make_convolve, METH_VARARGS,
      "Create 1D full convolution node: y = conv(kernel_param, child)"},
+    {"make_kron", py_make_kron, METH_VARARGS,
+     "Create Kronecker product node: Z = kron(A, B)"},
     {"make_matmul", py_make_matmul, METH_VARARGS,
      "Create matrix multiplication node (Z = X @ Y)"},
     {"make_param_scalar_mult", py_make_param_scalar_mult, METH_VARARGS,