Add backend to normcdf and normpdf calls in mixnorm (#100)

Author: cbuelt

scoringrules/core/crps/_closed.py

@@ -628,8 +628,12 @@ def mixnorm(
     s_X = B.sqrt(s[..., None] ** 2 + s[..., None, :] ** 2)
     w_X = w[..., None] * w[..., None, :]
 
-    A_y = m_y * (2 * _norm_cdf(m_y / s) - 1) + 2 * s * _norm_pdf(m_y / s)
-    A_X = m_X * (2 * _norm_cdf(m_X / s_X) - 1) + 2 * s_X * _norm_pdf(m_X / s_X)
+    A_y = m_y * (2 * _norm_cdf(m_y / s, backend=backend) - 1) + 2 * s * _norm_pdf(
+        m_y / s, backend=backend
+    )
+    A_X = m_X * (2 * _norm_cdf(m_X / s_X, backend=backend) - 1) + 2 * s_X * _norm_pdf(
+        m_X / s_X, backend=backend
+    )
 
     sc_1 = B.sum(w * A_y, axis=-1)
     sc_2 = B.sum(w_X * A_X, axis=(-1, -2))