DOC: Add docstrings to quantlib/math/array.pyx

This commit adds numpydoc-style docstrings to the `Array` class and its methods in `quantlib/math/array.pyx`.

The docstrings are based on the documentation from the original QuantLib C++ library and are adapted for Python style.

Author: google-labs-jules[bot]

quantlib/math/array.pyx

@@ -15,8 +15,17 @@ cimport numpy as np
 np.import_array()
 
 cdef class Array:
-    """
-    1D array for linear algebra
+    """1D array for linear algebra.
+
+    This class implements the concept of a vector as used in linear algebra.
+
+    Parameters
+    ----------
+    size : int, optional
+        The size of the array.
+    value : float, optional
+        The value to fill the array with.
+
     """
 
     def __init__(self, Size size=0, value=None):
@@ -39,6 +48,7 @@ cdef class Array:
         return self._thisptr.size()
 
     def to_ndarray(self):
+        """Returns a view of the array as a numpy array."""
         cdef np.npy_intp[1] dims
         dims[0] = self._thisptr.size()
         cdef arr = np.PyArray_SimpleNewFromData(1, &dims[0], np.NPY_DOUBLE, <void*>(self._thisptr.begin()))
@@ -47,10 +57,12 @@ cdef class Array:
         return arr
 
 cpdef qlarray_from_pyarray(p):
+    """Create a QuantLib Array from a Python array."""
     cdef Array x = Array(len(p))
     for i in range(len(p)):
         x._thisptr[i] = p[i]
     return x
 
 cpdef pyarray_from_qlarray(a):
+    """Create a Python array from a QuantLib Array."""
     return [a[i] for i in range(a.size)]