Merge branch 'qutip:master' into steadystate_floque_checks

doc/changes/2371.bugfix

@@ -0,0 +1,3 @@
+The import statement was added to import the partial_transpose function directly from the qutip module. This was done to fix the TypeError: 'module' object is not callable error.
+
+Added a condition that check if the input rho is a ket (a type of quantum state) and it also ensures that the negativity function can handle both kets and density operators as input.

qutip/entropy.py

@@ -4,7 +4,8 @@
 
 from numpy import conj, e, inf, imag, inner, real, sort, sqrt
 from numpy.lib.scimath import log, log2
-from . import (ptrace, ket2dm, tensor, sigmay, partial_transpose,
+from .partial_transpose import partial_transpose
+from . import (ptrace, tensor, sigmay, ket2dm,
                expand_operator)
 from .core import data as _data
 
@@ -129,6 +130,8 @@ def negativity(rho, subsys, method='tracenorm', logarithmic=False):
 
         Experimental.
     """
+    if rho.isket or rho.isbra:
+        rho = ket2dm(rho)
     mask = [idx == subsys for idx, n in enumerate(rho.dims[0])]
     rho_pt = partial_transpose(rho, mask)
 
@@ -140,6 +143,7 @@ def negativity(rho, subsys, method='tracenorm', logarithmic=False):
     else:
         raise ValueError("Unknown method %s" % method)
 
+# Return the negativity value (or its logarithm if specified)
     if logarithmic:
         return log2(2 * N + 1)
     else: