[NumPy] NumPy support for linalg.inv

python/mxnet/ndarray/numpy/linalg.py

@@ -21,7 +21,7 @@
 from . import _op as _mx_nd_np
 from . import _internal as _npi
 
-__all__ = ['norm', 'svd', 'cholesky']
+__all__ = ['norm', 'svd', 'cholesky', 'inv']
 
 
 def norm(x, ord=None, axis=None, keepdims=False):
@@ -200,3 +200,45 @@ def cholesky(a):
            [ 4., 10.]])
     """
     return _npi.cholesky(a)
+
+
+def inv(a):
+    r"""
+    Compute the (multiplicative) inverse of a matrix.
+
+    Given a square matrix `a`, return the matrix `ainv` satisfying
+    ``dot(a, ainv) = dot(ainv, a) = eye(a.shape[0])``.
+
+    Parameters
+    ----------
+    a : (..., M, M) ndarray
+        Matrix to be inverted.
+
+    Returns
+    -------
+    ainv : (..., M, M) ndarray
+        (Multiplicative) inverse of the matrix `a`.
+
+    Raises
+    ------
+    MXNetError
+        If `a` is not square or inversion fails.
+
+    Examples
+    --------
+    >>> from mxnet import np
+    >>> a = np.array([[1., 2.], [3., 4.]])
+    array([[-2. ,  1. ],
+           [ 1.5, -0.5]])
+
+    Inverses of several matrices can be computed at once:
+
+    >>> a = np.array([[[1., 2.], [3., 4.]], [[1, 3], [3, 5]]])
+    >>> np.linalg.inv(a)
+    array([[[-2.        ,  1.        ],
+            [ 1.5       , -0.5       ]],
+
+           [[-1.2500001 ,  0.75000006],
+            [ 0.75000006, -0.25000003]]])
+    """
+    return _npi.inv(a)

python/mxnet/numpy/linalg.py

@@ -20,7 +20,7 @@
 from __future__ import absolute_import
 from ..ndarray import numpy as _mx_nd_np
 
-__all__ = ['norm', 'svd', 'cholesky']
+__all__ = ['norm', 'svd', 'cholesky', 'inv']
 
 
 def norm(x, ord=None, axis=None, keepdims=False):
@@ -218,3 +218,45 @@ def cholesky(a):
            [ 4., 10.]])
     """
     return _mx_nd_np.linalg.cholesky(a)
+
+
+def inv(a):
+    r"""
+    Compute the (multiplicative) inverse of a matrix.
+
+    Given a square matrix `a`, return the matrix `ainv` satisfying
+    ``dot(a, ainv) = dot(ainv, a) = eye(a.shape[0])``.
+
+    Parameters
+    ----------
+    a : (..., M, M) ndarray
+        Matrix to be inverted.
+
+    Returns
+    -------
+    ainv : (..., M, M) ndarray
+        (Multiplicative) inverse of the matrix `a`.
+
+    Raises
+    ------
+    MXNetError
+        If `a` is not square or inversion fails.
+
+    Examples
+    --------
+    >>> from mxnet import np
+    >>> a = np.array([[1., 2.], [3., 4.]])
+    array([[-2. ,  1. ],
+           [ 1.5, -0.5]])
+
+    Inverses of several matrices can be computed at once:
+
+    >>> a = np.array([[[1., 2.], [3., 4.]], [[1, 3], [3, 5]]])
+    >>> np.linalg.inv(a)
+    array([[[-2.        ,  1.        ],
+            [ 1.5       , -0.5       ]],
+
+           [[-1.2500001 ,  0.75000006],
+            [ 0.75000006, -0.25000003]]])
+    """
+    return _mx_nd_np.linalg.inv(a)

python/mxnet/numpy_dispatch_protocol.py

@@ -126,6 +126,7 @@ def _run_with_array_ufunc_proto(*args, **kwargs):
     'zeros_like',
     'linalg.norm',
     'linalg.cholesky',
+    'linalg.inv',
     'trace',
     'tril',
     'meshgrid',

python/mxnet/symbol/numpy/linalg.py

@@ -22,7 +22,7 @@
 from . import _op as _mx_sym_np
 from . import _internal as _npi
 
-__all__ = ['norm', 'svd', 'cholesky']
+__all__ = ['norm', 'svd', 'cholesky', 'inv']
 
 
 def norm(x, ord=None, axis=None, keepdims=False):
@@ -187,3 +187,45 @@ def cholesky(a):
            [ 4., 10.]])
     """
     return _npi.cholesky(a)
+
+
+def inv(a):
+    r"""
+    Compute the (multiplicative) inverse of a matrix.
+
+    Given a square matrix `a`, return the matrix `ainv` satisfying
+    ``dot(a, ainv) = dot(ainv, a) = eye(a.shape[0])``.
+
+    Parameters
+    ----------
+    a : (..., M, M) ndarray
+        Matrix to be inverted.
+
+    Returns
+    -------
+    ainv : (..., M, M) ndarray
+        (Multiplicative) inverse of the matrix `a`.
+
+    Raises
+    ------
+    MXNetError
+        If `a` is not square or inversion fails.
+
+    Examples
+    --------
+    >>> from mxnet import np
+    >>> a = np.array([[1., 2.], [3., 4.]])
+    array([[-2. ,  1. ],
+           [ 1.5, -0.5]])
+
+    Inverses of several matrices can be computed at once:
+
+    >>> a = np.array([[[1., 2.], [3., 4.]], [[1, 3], [3, 5]]])
+    >>> np.linalg.inv(a)
+    array([[[-2.        ,  1.        ],
+            [ 1.5       , -0.5       ]],
+
+           [[-1.2500001 ,  0.75000006],
+            [ 0.75000006, -0.25000003]]])
+    """
+    return _npi.inv(a)

src/operator/linalg_impl.h

@@ -1598,7 +1598,8 @@ void linalg_batch_inverse<xpu, DType>(const Tensor<xpu, 3, DType>& A, \
     get_space_typed<xpu, 1, DType>(Shape1(workspace_size), s); \
   const Tensor<xpu, 2, int> pivot(reinterpret_cast<int *>(workspace.dptr_), \
                                   Shape2(A.size(0), A.size(1))); \
-  const Tensor<xpu, 3, DType> LU(reinterpret_cast<DType *>(pivot.dptr_ + pivot.MSize()), \
+  int offset = pivot.MSize() & 1 ? pivot.MSize() + 1 : pivot.MSize(); \
+  const Tensor<xpu, 3, DType> LU(reinterpret_cast<DType *>(pivot.dptr_ + offset), \
                                  A.shape_); \
   Copy(LU, B, s); \
   linalg_batch_getrf(LU, pivot, true, s); \

src/operator/tensor/la_op-inl.h

@@ -463,6 +463,9 @@ struct inverse {
                  const OpContext& ctx, const nnvm::NodeAttrs& attrs) {
     // Since inverse(A) = trans(inverse(trans(A))), so we don't need to transpose
     // A even if we are using the col-major version of getrf and getri routines.
+    if (B.shape_.Size() == 0U) {
+      return;
+    }
     linalg_batch_inverse(A, B, ctx);
   }
 };
@@ -882,6 +885,9 @@ struct inverse_backward {
                  const Tensor<xpu, 3, DType>& dB,
                  const OpContext& ctx, const nnvm::NodeAttrs& attrs) {
     // Backward of A = inverse(B)
+    if (dB.shape_.Size() == 0U) {
+      return;
+    }
     Stream<xpu> *s = ctx.get_stream<xpu>();
     Tensor<xpu, 3, DType> temp = ctx.requested[0]
       .get_space_typed<xpu, 3, DType>(A.shape_, s);

src/operator/tensor/la_op.cc

@@ -893,6 +893,7 @@ NNVM_REGISTER_OP(_backward_linalg_syevd)
 
 NNVM_REGISTER_OP(_linalg_inverse)
 .add_alias("linalg_inverse")
+.add_alias("_npi_inv")
 .describe(R"code(Compute the inverse of a matrix.
 Input is a tensor *A* of dimension *n >= 2*.
 

tests/python/unittest/test_numpy_interoperability.py

@@ -273,6 +273,11 @@ def _add_workload_linalg_cholesky():
         OpArgMngr.add_workload('linalg.cholesky', np.array(a, dtype=dtype))
 
 
+def _add_workload_linalg_inv():
+    OpArgMngr.add_workload('linalg.inv', np.array(_np.ones((0, 0)), dtype=np.float32))
+    OpArgMngr.add_workload('linalg.inv', np.array(_np.ones((0, 1, 1)), dtype=np.float64))
+
+
 def _add_workload_trace():
     OpArgMngr.add_workload('trace', np.random.uniform(size=(4, 1)))
     OpArgMngr.add_workload('trace', np.random.uniform(size=(3, 2)))
@@ -1216,6 +1221,7 @@ def _prepare_workloads():
     _add_workload_zeros_like(array_pool)
     _add_workload_linalg_norm()
     _add_workload_linalg_cholesky()
+    _add_workload_linalg_inv()
     _add_workload_trace()
     _add_workload_tril()
     _add_workload_outer()

tests/python/unittest/test_numpy_op.py

@@ -1669,7 +1669,7 @@ def hybrid_forward(self, F, a, b, *args, **kwargs):
         mx_test_x1 = mx.numpy.array(np_test_x1, dtype=ltype)
         mx_test_x2 = mx.numpy.array(np_test_x2, dtype=rtype)
         rtol = 1e-2 if ltype is np.float16 or rtype is np.float16 else 1e-3
-        atol = 1e-4 if ltype is np.float16 or rtype is np.float16 else 1e-5
+        atol = 1e-3 if ltype is np.float16 or rtype is np.float16 else 1e-5
         for hybridize in [True, False]:
             if hybridize:
                 mx_func.hybridize()
@@ -3046,6 +3046,84 @@ def check_cholesky(L, data_np):
         check_cholesky(L, data_np)
 
 
+@with_seed()
+@use_np
+def test_np_linalg_inv():
+    class TestInverse(HybridBlock):
+        def __init__(self):
+            super(TestInverse, self).__init__()
+
+        def hybrid_forward(self, F, data):
+            return F.np.linalg.inv(data)
+
+    def get_grad(A):
+        if 0 in A.shape:
+            return A
+
+        dA = _np.ones_like(A)
+        A_inv = _np.linalg.inv(A)
+        dA_inv = -_np.matmul(_np.matmul(A_inv, dA), A_inv)
+        return _np.swapaxes(dA_inv, -1, -2)
+
+    def check_inv(A_inv, data_np):
+        assert A_inv.shape == data_np.shape
+        # catch error if numpy throws rank < 2
+        try:
+            A_expected = _np.linalg.inv(data_np)
+        except Exception as e:
+            print(data_np)
+            print(data_np.shape)
+            print(e)
+        else:
+            assert A_inv.shape == A_expected.shape
+            assert_almost_equal(A_inv.asnumpy(), A_expected, rtol=rtol, atol=atol)
+
+    shapes = [
+        (0, 0),
+        (4, 4),
+        (2, 2),
+        (1, 1),
+        (2, 1, 1),
+        (0, 1, 1),
+        (6, 1, 1),
+        (2, 3, 3, 3),
+        (4, 2, 1, 1),
+        (0, 5, 3, 3),
+        (5, 0, 0, 0),
+        (3, 3, 0, 0),
+        (3, 5, 5),
+    ]
+    dtypes = ['float32', 'float64']
+    for hybridize, dtype, shape in itertools.product([True, False], dtypes, shapes):
+        atol = rtol = 1e-2
+
+        test_inv = TestInverse()
+        if hybridize:
+            test_inv.hybridize()
+        # use LU decomposition to generate invertible matrices
+        if 0 in shape:
+            data_np = _np.ones(shape)
+        else:
+            n = shape[-1]
+            L = _np.tril(_np.random.uniform(-10., 10., shape))
+            U = _np.triu(_np.random.uniform(-10., 10., shape))
+            data_np = _np.matmul(L, U)
+        data = np.array(data_np, dtype=dtype)
+        data.attach_grad()
+        with mx.autograd.record():
+            A_inv = test_inv(data)
+
+        # check cholesky validity
+        check_inv(A_inv, data_np)
+        # check backward. backward does not support empty input
+        mx.autograd.backward(A_inv)
+        backward_expected = get_grad(data.asnumpy())
+        assert_almost_equal(data.grad.asnumpy(), backward_expected, rtol=rtol, atol=atol)
+        # check imperative once again
+        A_inv = np.linalg.inv(data)
+        check_inv(A_inv, data_np)
+
+
 @with_seed()
 @use_np
 def test_np_vstack():