Allow any negative number in the knot-vector (#476)

* Allow any negative number in the knot-vector

This resolves #475

* use lowest() instead of min() to avoid edge case

* adding test case for spline construction with uniform unclamped knots

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: Sebastian Bachmann <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 3 people

src/py/py_spline.cpp

@@ -23,6 +23,7 @@ SOFTWARE.
 */
 
 #include <algorithm>
+#include <limits>
 #include <memory>
 #include <numeric>
 #include <string>
@@ -106,7 +107,7 @@ void PySpline::NewCore(const py::kwargs& kwargs) {
       knot_vector.reserve(n_knots);
 
       int nknots{0};
-      prev_knot = -1.;
+      prev_knot = std::numeric_limits<double>::lowest();
       for (py::handle k : kvs[i_para]) {
         this_knot = k.cast<double>();
 

tests/test_spline_constructors.py

@@ -14,6 +14,15 @@ def test_BSplines(np_rng):
         knot_vectors=[[0, 0, 1, 1], [0, 0, 0.4, 0.5, 0.7, 1, 1]],
         control_points=np_rng.random((10, 2)),
     )
+    # No assertion query; unclamped, uniform knot-vector
+    splinepy.BSpline(
+        degrees=[2, 2],
+        knot_vectors=[
+            [-4, -3, -2, -1, 0, 1, 2, 3, 4],
+            [-15, -10, -5, 0, 5, 10, 15],
+        ],
+        control_points=np_rng.random((6 * 4, 2)),
+    )
     # Check control points
     with pytest.raises(
         RuntimeError,