[MRG] Fix bug in emd2 with empty weighs on backends (PythonOT#606)

* fix buf emd2 for empty inputs

* update release file

* debug problems in optimization hen using list_to_arry by removing it everywhere

* update jax config in tests

* hopefully final fix

RELEASES.md

@@ -1,6 +1,6 @@
 # Releases
 
-## 0.9.3
+## 0.9.3dev
 
 #### New features
 + `ot.gromov._gw.solve_gromov_linesearch` now has an argument to specifify if the matrices are symmetric in which case the computation can be done faster.
@@ -9,6 +9,7 @@
 - Fixed an issue with cost correction for mismatched labels in `ot.da.BaseTransport` fit methods. This fix addresses the original issue introduced PR #587 (PR #593)
 - Fix gpu compatibility of sr(F)GW solvers when `G0 is not None`(PR #596)
 - Fix doc and example for lowrank sinkhorn (PR #601)
+- Fix issue with empty weights for `ot.emd2` (PR #606, Issue #534)
 
 ## 0.9.2
 *December 2023*

ot/__init__.py

@@ -58,7 +58,7 @@
 # utils functions
 from .utils import dist, unif, tic, toc, toq
 
-__version__ = "0.9.3"
+__version__ = "0.9.3dev"
 
 __all__ = ['emd', 'emd2', 'emd_1d', 'sinkhorn', 'sinkhorn2', 'utils',
            'datasets', 'bregman', 'lp', 'tic', 'toc', 'toq', 'gromov',

ot/gromov/_gw.py

@@ -703,8 +703,6 @@ def solve_gromov_linesearch(G, deltaG, cost_G, C1, C2, M, reg,
 
     """
     if nx is None:
-        G, deltaG, C1, C2, M = list_to_array(G, deltaG, C1, C2, M)
-
         if isinstance(M, int) or isinstance(M, float):
             nx = get_backend(G, deltaG, C1, C2)
         else:

ot/gromov/_semirelaxed.py

@@ -583,8 +583,6 @@ def solve_semirelaxed_gromov_linesearch(G, deltaG, cost_G, C1, C2, ones_p,
             Gromov-Wasserstein". NeurIPS 2023 Workshop OTML.
     """
     if nx is None:
-        G, deltaG, C1, C2, M = list_to_array(G, deltaG, C1, C2, M)
-
         if isinstance(M, int) or isinstance(M, float):
             nx = get_backend(G, deltaG, C1, C2)
         else:

ot/lp/__init__.py

@@ -302,17 +302,24 @@ def emd(a, b, M, numItermax=100000, log=False, center_dual=True, numThreads=1, c
     ot.optim.cg : General regularized OT
     """
 
-    # convert to numpy if list
     a, b, M = list_to_array(a, b, M)
+    nx = get_backend(M, a, b)
 
-    a0, b0, M0 = a, b, M
-    if len(a0) != 0:
-        type_as = a0
-    elif len(b0) != 0:
-        type_as = b0
+    if len(a) != 0:
+        type_as = a
+    elif len(b) != 0:
+        type_as = b
     else:
-        type_as = M0
-    nx = get_backend(M0, a0, b0)
+        type_as = M
+
+    # if empty array given then use uniform distributions
+    if len(a) == 0:
+        a = nx.ones((M.shape[0],), type_as=type_as) / M.shape[0]
+    if len(b) == 0:
+        b = nx.ones((M.shape[1],), type_as=type_as) / M.shape[1]
+
+    # store original tensors
+    a0, b0, M0 = a, b, M
 
     # convert to numpy
     M, a, b = nx.to_numpy(M, a, b)
@@ -474,15 +481,23 @@ def emd2(a, b, M, processes=1,
     """
 
     a, b, M = list_to_array(a, b, M)
+    nx = get_backend(M, a, b)
 
-    a0, b0, M0 = a, b, M
-    if len(a0) != 0:
-        type_as = a0
-    elif len(b0) != 0:
-        type_as = b0
+    if len(a) != 0:
+        type_as = a
+    elif len(b) != 0:
+        type_as = b
     else:
-        type_as = M0
-    nx = get_backend(M0, a0, b0)
+        type_as = M
+
+    # if empty array given then use uniform distributions
+    if len(a) == 0:
+        a = nx.ones((M.shape[0],), type_as=type_as) / M.shape[0]
+    if len(b) == 0:
+        b = nx.ones((M.shape[1],), type_as=type_as) / M.shape[1]
+
+    # store original tensors
+    a0, b0, M0 = a, b, M
 
     # convert to numpy
     M, a, b = nx.to_numpy(M, a, b)
@@ -491,11 +506,6 @@ def emd2(a, b, M, processes=1,
     b = np.asarray(b, dtype=np.float64)
     M = np.asarray(M, dtype=np.float64, order='C')
 
-    # if empty array given then use uniform distributions
-    if len(a) == 0:
-        a = np.ones((M.shape[0],), dtype=np.float64) / M.shape[0]
-    if len(b) == 0:
-        b = np.ones((M.shape[1],), dtype=np.float64) / M.shape[1]
 
     assert (a.shape[0] == M.shape[0] and b.shape[0] == M.shape[1]), \
         "Dimension mismatch, check dimensions of M with a and b"

ot/lp/solver_1d.py

@@ -223,8 +223,12 @@ def emd_1d(x_a, x_b, a=None, b=None, metric='sqeuclidean', p=1., dense=True,
     ot.lp.emd2_1d : EMD for 1d distributions (returns cost instead of the
         transportation matrix)
     """
-    a, b, x_a, x_b = list_to_array(a, b, x_a, x_b)
+    x_a, x_b = list_to_array(x_a, x_b)
     nx = get_backend(x_a, x_b)
+    if a is not None:
+        a = list_to_array(a, nx=nx)
+    if b is not None:
+        b = list_to_array(b, nx=nx)
 
     assert (x_a.ndim == 1 or x_a.ndim == 2 and x_a.shape[1] == 1), \
         "emd_1d should only be used with monodimensional data"

ot/optim.py

@@ -12,7 +12,6 @@
 import warnings
 from .lp import emd
 from .bregman import sinkhorn
-from .utils import list_to_array
 from .backend import get_backend
 
 with warnings.catch_warnings():
@@ -73,7 +72,6 @@ def line_search_armijo(
 
     """
     if nx is None:
-        xk, pk, gfk = list_to_array(xk, pk, gfk)
         xk0, pk0 = xk, pk
         nx = get_backend(xk0, pk0)
     else:
@@ -236,7 +234,7 @@ def generic_conditional_gradient(a, b, M, f, df, reg1, reg2, lp_solver, line_sea
     ot.lp.emd : Unregularized optimal transport
     ot.bregman.sinkhorn : Entropic regularized optimal transport
     """
-    a, b, M, G0 = list_to_array(a, b, M, G0)
+
     if isinstance(M, int) or isinstance(M, float):
         nx = get_backend(a, b)
     else:

ot/utils.py

@@ -56,12 +56,30 @@ def laplacian(x):
     return L
 
 
-def list_to_array(*lst):
+def list_to_array(*lst, nx=None):
     r""" Convert a list if in numpy format """
+    lst_not_empty = [a for a in lst if len(a) > 0 and not isinstance(a, list)]
+    if nx is None:  # find backend
+
+        if len(lst_not_empty) == 0:
+            type_as = np.zeros(0)
+            nx = get_backend(type_as)
+        else:
+            nx = get_backend(*lst_not_empty)
+            type_as = lst_not_empty[0]
+    else:
+        if len(lst_not_empty) == 0:
+            type_as = None
+        else:
+            type_as = lst_not_empty[0]
     if len(lst) > 1:
-        return [np.array(a) if isinstance(a, list) else a for a in lst]
+        return [nx.from_numpy(np.array(a), type_as=type_as)
+                if isinstance(a, list) else a for a in lst]
     else:
-        return np.array(lst[0]) if isinstance(lst[0], list) else lst[0]
+        if isinstance(lst[0], list):
+            return nx.from_numpy(np.array(lst[0]), type_as=type_as)
+        else:
+            return lst[0]
 
 
 def proj_simplex(v, z=1):

test/conftest.py

@@ -13,7 +13,7 @@
 
 if jax:
     os.environ['XLA_PYTHON_CLIENT_PREALLOCATE'] = 'false'
-    from jax.config import config
+    from jax import config
     config.update("jax_enable_x64", True)
 
 if tf:

test/test_ot.py

@@ -74,7 +74,11 @@ def test_emd2_backends(nx):
 
     valb = ot.emd2(ab, ab, Mb)
 
+    # check with empty inputs
+    valb2 = ot.emd2([], [], Mb)
+
     np.allclose(val, nx.to_numpy(valb))
+    np.allclose(val, nx.to_numpy(valb2))
 
 
 def test_emd_emd2_types_devices(nx):

test/test_utils.py

@@ -322,6 +322,18 @@ def test_cost_normalization(nx):
         ot.utils.cost_normalization(C1, 'error')
 
 
+def test_list_to_array(nx):
+
+    lst = [np.array([1, 2, 3]), np.array([4, 5, 6])]
+
+    a1, a2 = ot.utils.list_to_array(*lst)
+
+    assert a1.shape == (3,)
+    assert a2.shape == (3,)
+
+    a, b, M = ot.utils.list_to_array([], [], [[1.0, 2.0], [3.0, 4.0]])
+
+
 def test_check_params():
 
     res1 = ot.utils.check_params(first='OK', second=20)