fixes here and there, doc

_test_scalar_opt.py

@@ -42,7 +42,7 @@ class _test_opts(unittest.TestCase):
 #         x, y, z = inputs()
 #         a, b, c, d = more_inputs()
 # #        e = (2.0 * x) / (2.0 * y)
-# #        e = (2.0 * x) / (4.0 * y)
+#         e = (2.0 * x) / (4.0 * y)
 # #        e = x / (y / z)
 # #        e = (x * y) / x
 # #        e = (x / y) * (y / z) * (z / x)
@@ -71,11 +71,12 @@ class _test_opts(unittest.TestCase):
 # #        e = (a - b) + (b - c) + (c - d)
 # #        e = x + -y
 # #        e = a - b - b + a + b + c + b - c
-#         e = x + log(y) - x + y
+# #        e = x + log(y) - x + y
+#         e = 2.0 + x + 4.0
 #         g = Env([x, y, z, a, b, c, d], [e])
 #         print g
 #         gof.ConstantFinder().optimize(g)
-#         addfn = lambda *inputs: reduce(lambda x, y: x + y, (0,) + inputs)
+#         addfn = lambda *inputs: sum(inputs)
 #         subfn = lambda x, y: x - y
 #         negfn = lambda x: -x
 #         Canonizer(Add, Sub, Neg, addfn, subfn, negfn).optimize(g)

base_tensor.py

@@ -58,7 +58,7 @@ class BaseTensor(Result):
     # filter
     #
     def filter(self, arr):
-        """cast to an L{numpy.ndarray} and ensure arr has correct rank, shape"""
+        """Cast to an L{numpy.ndarray} and ensure arr has correct rank and shape."""
         if not (isinstance(arr, numpy.ndarray) \
                 and arr.dtype==self.dtype):
             arr = numpy.asarray(arr, dtype = self.dtype)
@@ -102,6 +102,9 @@ class BaseTensor(Result):
     # Description for constant folding
     #
     def desc(self):
+        """
+        Returns a hashable description of this BaseTensor.
+        """
         if self.data is not None:
             return (BaseTensor, self.dtype, self.broadcastable, self.data.data[:])
         else:
@@ -210,6 +213,7 @@ class BaseTensor(Result):
         };
         """
         return template % dict(nbits = 64, half_nbits = 32) + template % dict(nbits = 128, half_nbits = 64)
+        # todo: use C templating
 
 
     ############################

opt.py

@@ -7,6 +7,19 @@ import scalar
 
 
 class InplaceOptimizer(opt.OpSpecificOptimizer):
+    """
+    Usage: inplace_optimizer.optimize(env)
+    
+    Attempts to replace all Broadcast ops by versions of them
+    that operate inplace. It operates greedily: for each Broadcast
+    Op that is encountered, for each output, tries each input to
+    see if it can operate inplace on that input. If so, makes the
+    change and go to the next output or Broadcast Op.
+
+    Examples:
+      x + y + z -> x += y += z
+      (x + y) * (x * y) -> (x += y) *= (x * y) or (x + y) *= (x *= y)
+    """
 
     opclass = Broadcast
     
@@ -24,6 +37,7 @@ class InplaceOptimizer(opt.OpSpecificOptimizer):
                     continue
                 candidate_inputs.remove(candidate_input)
                 op = new_op
+                baseline = inplace_pattern
                 break
 
 inplace_optimizer = InplaceOptimizer()
@@ -32,6 +46,8 @@ inplace_optimizer = InplaceOptimizer()
 
 class DimShuffleLifter(opt.Optimizer):
     """
+    Usage: lift_dimshuffle.optimize(env)
+    
     "Lifts" DimShuffle through Broadcast operations and merges
     consecutive DimShuffles. Basically, applies the following
     transformations on the whole graph:
@@ -47,9 +63,6 @@ class DimShuffleLifter(opt.Optimizer):
 
         seen = set()
         
-        def merge(ord1, ord2):
-            return [x == 'x' and 'x' or ord1[x] for x in ord2]
-        
         def lift(r):
             if r in seen:
                 return
@@ -62,6 +75,7 @@ class DimShuffleLifter(opt.Optimizer):
             if isinstance(op, DimShuffle):
                 in_op = op.inputs[0].owner
                 if isinstance(in_op, DimShuffle):
+                    # DimShuffle(DimShuffle(x)) => DimShuffle(x)
                     new_order = [x == 'x' and 'x' or in_op.new_order[x] for x in op.new_order]
                     if new_order == range(len(new_order)):
                         repl = in_op.inputs[0]
@@ -71,6 +85,7 @@ class DimShuffleLifter(opt.Optimizer):
                     lift(repl)
                     return
                 elif isinstance(in_op, Broadcast):
+                    # DimShuffle(Broadcast(x, y)) => Broadcast(DimShuffle(x), DimShuffle(y))
                     repl = Broadcast(in_op.scalar_opclass,
                                      [DimShuffle(input, op.new_order).out for input in in_op.inputs],
                                      in_op.inplace_pattern).out
@@ -87,9 +102,24 @@ lift_dimshuffle = DimShuffleLifter()
 
 
 def find_cliques(env, through_broadcast = False):
+    """
+    Usage: find_cliques(env, through_broadcast = False)
 
+    Returns a list of pairs where each pair contains a list
+    of inputs and a list of outputs such that Env(inputs, outputs)
+    contains nothing but Broadcast Ops.
+
+    If through_broadcast is False, the cliques will only be
+    allowed to broadcast over the inputs, which means, for
+    example, that vector operations will not be mixed with
+    matrix operations.
+    """
 
     def seek_from(r):
+        # walks through the graph until it encounters a
+        # non-Broadcast operation or (if through_broadcast
+        # is False) a Result which needs to be broadcasted.
+        
         op = r.owner
         if r in env.inputs \
                 or r in env.orphans() \
@@ -103,6 +133,10 @@ def find_cliques(env, through_broadcast = False):
         ret = set()
 
         if not through_broadcast:
+            # check each dimension over all the inputs - if the broadcastable
+            # fields are not all 0 or all 1 for a particular dimension, then
+            # broadcasting will be performed along it on the inputs where the
+            # value is 1 and we will stop.
             if any(any(bc) and not all(bc)
                    for bc in zip(*[input.broadcastable for input in op.inputs])):
                 ret.update(op.inputs)
@@ -111,6 +145,7 @@ def find_cliques(env, through_broadcast = False):
         for input in op.inputs:
             res = seek_from(input)
             if res is None:
+                # input is a leaf of our search
                 ret.add(input)
             else:
                 ret.update(res)
@@ -124,11 +159,14 @@ def find_cliques(env, through_broadcast = False):
             return
         clique_inputs = seek_from(r)
         if clique_inputs is None:
+            # Not in a clique, keep going
             op = r.owner
             if op is not None:
                 for input in op.inputs:
                     find_cliques_helper(input)
         else:
+            # We found a clique, add it to the list and
+            # jump to the leaves.
             cliques.append((clique_inputs, [r]))
             for input in clique_inputs:
                 find_cliques_helper(input)
@@ -142,6 +180,24 @@ def find_cliques(env, through_broadcast = False):
 
 
 class CliqueOptimizer(opt.Optimizer):
+    """
+    Usage: CliqueOptimizer(through_broadcast = False,
+                           scalar_optimizer = None,
+                           make_composite = False).optimize(env)
+
+    Finds cliques of Broadcast operations in the env and does either
+    or both of two things:
+    
+    * Apply scalar_optimizer on the clique as if the clique was a
+      group of scalar operations. scalar_optimizer can be any optimization
+      which applies on scalars. If it is None, no optimization is done.
+    * Replace the clique with a single Op, optimized to perform the
+      computations properly. If make_composite is False, no such replacement
+      is done.
+
+    Note: it is recommended to run the lift_dimshuffle optimization before
+    this one.
+    """
 
     def __init__(self, through_broadcast = False, scalar_optimizer = None, make_composite = False):
         self.through_broadcast = through_broadcast
@@ -152,20 +208,25 @@ class CliqueOptimizer(opt.Optimizer):
         if self.scalar_optimizer is None and not self.make_composite:
             # there's nothing to do with the cliques...
             return
+        
         cliques = find_cliques(env, self.through_broadcast)
         opt = self.scalar_optimizer
 
         def build_scalar_clique(r, env, equiv):
+            # Maps a clique of Broadcast Ops to a clique of Scalar Ops with the same
+            # structure and equivalent operations. equiv contains the mapping.
             if r in equiv:
                 return equiv[r]
             op = r.owner
             if r in env.inputs or r in env.orphans():
+                # For each leave we make a Scalar of the corresponding dtype
                 s = scalar.Scalar(dtype = r.dtype)
                 _r = r
                 if isinstance(r.owner, DimShuffle) and all(x == 'x' for x in r.owner.new_order):
                     _r = r.owner.inputs[0]
                 if (getattr(r, 'constant', False) or getattr(_r, 'constant', False)) \
                        and _r.broadcastable == ():
+                    # If we have a constant tensor we map it to a constant scalar.
                     s.data = _r.data
                     s.constant = True
                 equiv[r] = s
@@ -184,15 +245,18 @@ class CliqueOptimizer(opt.Optimizer):
             s_g = Env([equiv[r] for r in g.inputs],
                       [equiv[r] for r in g.outputs])
             if opt is not None:
-                equiv2 = dict()
+                equiv2 = dict() # reverse mapping, from Scalar Op to Tensor Op
                 for k, v in equiv.items():
                     equiv2[v] = k
                 def transform(op, equiv):
+                    # We get a scalar op and we return an equivalent op on tensors.
                     return Broadcast(op.__class__, [equiv[input] for input in op.inputs])
-                s_g.add_feature(sync_to(env, equiv2, transform))
+                s_g.add_feature(sync_to(env, equiv2, transform)) # Any change to s_g will now be transferred to g
                 opt.optimize(s_g)
             if self.make_composite:
                 def follow_inplace(r):
+                    # Tries to find the earliest r2 in g such that r destroys r2
+                    # If no such r2 is found, returns None
                     op = r.owner
                     if op is None or r in g.inputs or r in g.orphans():
                         return None
@@ -211,6 +275,8 @@ class CliqueOptimizer(opt.Optimizer):
                 for i, output in enumerate(g.outputs):
                     destroyed = follow_inplace(output)
                     if destroyed is not None and destroyed in g.inputs:
+                        # we transfer the inplace operation only if it is
+                        # an input that is destroyed
                         inplace_pattern[i] = g.inputs.index(destroyed)
                 C = scalar.composite(s_g.inputs, s_g.outputs)
                 ec = Broadcast(C, g.inputs, inplace_pattern = inplace_pattern)
@@ -218,6 +284,17 @@ class CliqueOptimizer(opt.Optimizer):
 
 
 def sync_to(target, equiv, transform):
+    """
+    Usage: sync_to(target, equiv, transform)
+    * target: an Env
+    * equiv: a dictionary that maps results and ops to results and ops
+             in target
+    * transform: a function that takes (op, equiv) as inputs and
+                 returns a new op.
+    
+    Returns a Feature that can be added to an Env and mirrors all
+    modifications to that env with modifications to the target env.
+    """
 
     class Synchronize(gof.Listener, gof.Constraint):
 
@@ -259,44 +336,3 @@ def sync_to(target, equiv, transform):
 
     return Synchronize
 
-
-
-
-
-
-
-
-
-
-
-"""
-This variable is used in compile.prog as the optimizer for all programs built
-using either compile.single, compile.to_func, and compile.prog.
-
-Old code::
-	if 0:
-	    def optimizer(lst):
-	        begin = gof.SeqOptimizer([])
-	        end   = gof.SeqOptimizer([gof.DummyRemover])
-	        seq_opt = gof.SeqOptimizer(begin + lst + end)
-	        return gof.PythonOpt(gof.MergeOptMerge(seq_opt))
-	
-	if 0:
-	    optimizer_begin = gof.SeqOptimizer([opt for name, opt in [
-	             ['double_transpose_eliminator', pattern_opt((transpose, (transpose, 'x')), 'x')],
-	
-	             ['addxx_to_twice',              pattern_opt((add_elemwise, 'x', 'x'), (twice, 'x'))],
-	
-	             ['twice_to_itwice',             op_sub(twice, itwice)],
-	
-	             ['mulxx_to_sqr',                pattern_opt((mul_elemwise, 'x', 'x'), (sqr, 'x'))],
-	
-	             ['sqr_to_isqr',                 op_sub(sqr, isqr)],
-	
-	             ['add_to_iadd',                 op_sub(add_elemwise, iadd_elemwise)],
-	
-	             ['add_to_iadd_reverse',         pattern_opt((add_elemwise, 'x', 'y'),
-	                 (iadd_elemwise, 'y', 'x'))]]])
-	#         ['remove_copies',               gof.OpRemover(array_copy)],
-	#         [None,                          gof.DummyRemover] # has to be at the end
-"""

scalar_opt.py

@@ -23,6 +23,39 @@ logpow = Pattern((Log, (Pow, 'x', 'y')),
 
 
 class Canonizer(gof.Optimizer):
+    """
+    Simplification tool.
+
+    Usage: Canonizer(main, inverse, reciprocal, mainfn, invfn, recfn, transform)
+    
+    * main: a suitable Op class that is commutative, associative and takes
+            one to an arbitrary number of inputs, e.g. Add or Mul
+    * inverse: an Op class such that inverse(main(x, y), y) == x
+               e.g. Sub or Div
+    * reciprocal: a function such that main(x, reciprocal(y)) == inverse(x, y)
+                  e.g. Neg or Inv
+
+    * mainfn, invfn, recfn: functions that behave just like the previous three
+                            Ops, but on true scalars (e.g. their impl)
+
+    * transform: a function that maps (numerator, denominatur) where numerator
+                 and denominator are lists of Result instances, to new lists
+                 where further simplifications may have been applied.
+
+    Examples:
+      add_canonizer = Canonizer(Add, Sub, Neg, lambda *inputs: sum(inputs), ...)
+      mul_canonizer = Canonizer(Mul, Div, Inv, lambda *inputs: product(inputs), ...)
+    
+    Examples of optimizations mul_canonizer can perform:
+      x / x -> 1
+      (x * y) / x -> y
+      x / y / x -> 1 / y
+      x / y / z -> x / (y * z)
+      x / (y / z) -> (x * z) / y
+      (a / b) * (b / c) * (c / d) -> a / d
+      (2.0 * x) / (4.0 * y) -> (0.5 * x) / y
+      2 * x / 2 -> x
+    """
 
     def __init__(self, main, inverse, reciprocal, mainfn, invfn, recfn, transform = None):
         self.main = main
@@ -37,10 +70,15 @@ class Canonizer(gof.Optimizer):
     def apply(self, env):
 
         def canonize(r):
+            
             if r in env.inputs or r in env.orphans():
                 return
             
             def flatten(r, nclients_check = True):
+                # Collapses a tree of main/inverse/reciprocal Ops (aka Mul/Div/Inv or Add/Sub/Neg)
+                # into a list of numerators and a list of denominators
+                # e.g. (x*(1/y))*(x/(z/a)) aka Mul(Mul(x, (Inv, y)), Div(x, Div(z, a))) -> [x, x, a], [z, y]
+                
                 op = r.owner
                 if op is None or r in env.inputs or r in env.orphans():
                     return [r], []
@@ -50,9 +88,11 @@ class Canonizer(gof.Optimizer):
                     nums = [x[0] for x in results]
                     denums = [x[1] for x in results]
                 elif isinstance(op, self.inverse) and (not nclients_check or env.nclients(r) == 1):
+                    # num, denum of the second argument are added to the denum, num respectively
                     nums = [results[0][0], results[1][1]]
                     denums = [results[0][1], results[1][0]]
                 elif isinstance(op, self.reciprocal) and (not nclients_check or env.nclients(r) == 1):
+                    # num, denum of the sole argument are added to the denum, num respectively
                     nums = [results[0][1]]
                     denums = [results[0][0]]
                 else:
@@ -70,22 +110,29 @@ class Canonizer(gof.Optimizer):
                         canonize(input)
                     return
 
+            # Terms that are both in the num and denum lists cancel each other
             for d in list(denum):
                 if d in list(num):
+                    # list.remove only removes the element once
                     num.remove(d)
                     denum.remove(d)
 
+            # We identify the constants in num and denum
             numct, num = utils.partition(lambda factor: getattr(factor, 'constant', False) and factor.data is not None, num)
             denumct, denum = utils.partition(lambda factor: getattr(factor, 'constant', False) and factor.data is not None, denum)
 
+            # All constants in num and denum are combined into a single constant which we add to num (unless it's a neutral constant)
             v = self.invfn(self.mainfn(*[x.data for x in numct]), self.mainfn(*[x.data for x in denumct]))
             if v != self.neutral:
                 num.insert(0, C(v))
 
+            # We optimize the num and denum lists further if requested
             if self.transform is not None:
                 num, denum = self.transform(env, num, denum)
 
             def make(factors):
+                # Combines the factors using self.main (aka Mul) depending
+                # on the number of elements.
                 n = len(factors)
                 if n == 0:
                     return None
@@ -98,10 +145,13 @@ class Canonizer(gof.Optimizer):
             
             if numr is None:
                 if denumr is None:
+                    # Everything cancelled each other so we're left with
+                    # the neutral element.
                     new_r = Scalar(dtype = r.dtype)
                     new_r.constant = True
                     new_r.data = self.neutral
                 else:
+                    # There's no numerator so we use reciprocal
                     new_r = self.reciprocal(denumr).out
             else:
                 if denumr is None:
@@ -109,6 +159,7 @@ class Canonizer(gof.Optimizer):
                 else:
                     new_r = self.inverse(numr, denumr).out
 
+            # Hopefully this won't complain!
             env.replace(r, new_r)
 
             for factor in num + denum:
@@ -119,11 +170,28 @@ class Canonizer(gof.Optimizer):
 
 
 def group_powers(env, num, denum):
+    """
+    Plugin for Canonizer: use as Canonizer(..., transform = group_powers)
+
+    Takes num, denum such that mul(*num) / mul(*denum) is in env
+    and searches for instances of exp(x) or x**y in order to group
+    together powers of the same variable. Returns num2, denum2 in
+    which the grouping has been done.
 
+    Note: this function does not modify env.
+
+    Examples:
+      group_powers([x, exp(x), exp(y)], [exp(z)]) -> [x, exp(x+y-z)], []
+    """
+
+    # maps a base to the list of powers it is raised to in the
+    # numerator/denominator lists.
     num_powers = {}
     denum_powers = {}
 
     def populate(d, seq):
+        # For each instance of exp or pow in seq, removes it from seq
+        # and does d[base].append(power).
         for factor in list(seq):
             op = factor.owner
             if op is None or factor in env.inputs or factor in env.orphans():
@@ -139,6 +207,8 @@ def group_powers(env, num, denum):
     populate(denum_powers, denum)
     
     for x in set(num_powers.keys() + denum_powers.keys()):
+        # we append base ** (num_powers[base] - denum_powers[base])
+        # to the num list
         
         try: num_ys = num_powers.pop(x)
         except KeyError: num_ys = []
@@ -148,6 +218,7 @@ def group_powers(env, num, denum):
 
         num_r = num_ys and add(*num_ys) or C(0)
         denum_r = denum_ys and add(*denum_ys) or C(0)
+        
         if x == 'e':
             num.append(exp(num_r - denum_r))
         else:

tensor.py

@@ -80,17 +80,14 @@ def astensor(data, broadcastable=None, name=None):
     if isinstance(data, BaseTensor):
         if broadcastable is not None and list(data.broadcastable) != list(broadcastable):
             raise TypeError("The data to wrap as a Tensor has the wrong broadcastable pattern. Expected %s, got %s." % (broadcastable, data.broadcastable))
-        if isinstance(data, Tensor) and (name is None or name == data.name):
+        if name is not None and name != data.name:
+            raise ValueError("Cannot rename an existing Tensor.")
         return data
-        else:
-            t = Tensor(data.dtype, data.broadcastable, name = name)
-            t.data = data
-            return t
     elif isinstance(data, Result):
-        data = data.data
+        raise TypeError("Cannot make a Tensor out of a non-Tensor result.")
         
     if data is None and broadcastable is None:
-        raise TypeError("Cannot make a Tensor out of None or a Result with no data.")
+        raise TypeError("Cannot make a Tensor out of None.")
     
     data = numpy.asarray(data)
     if broadcastable is None:
@@ -107,38 +104,6 @@ s2t.astensor = astensor
 # Supporting Ops
 ############################
 
-def _scalar_switch(normal_f, scalar_f, scalar_f_reverse = None):
-    """a decorator for operators before broadcasting works properly"""
-    def f(x, y):
-        def as_tensor(obj):
-            if isinstance(obj, Tensor):
-                return obj
-            else:
-                return astensor(obj)
-        x, y = as_tensor(x), as_tensor(y)
-        if 0 not in y.broadcastable:
-            return scalar_f(x, y)
-        if 0 not in x.broadcastable:
-            if scalar_f_reverse:
-                return scalar_f_reverse(y, x)
-            else:
-                raise TypeError("You cannot do this operation on a scalar.")
-        return normal_f(x, y)
-    return f
-
-def _assert_same_shapes(x, *rest):
-    """Ensure that all inputs to the function impl have the same size (foils numpy's broadcasting)"""
-    shape = x.shape
-    for other in rest:
-        if other.shape != shape:
-            raise ValueError(_assert_same_shapes.E_shape, shape, other.shape)
-_assert_same_shapes.E_shape = "The dimensions of the inputs do not match."
-
-def _assert_tensor_scalar(x, a):
-    """ensure that the second input is a scalar"""
-    if numpy.product(a.shape) != 1:
-        raise ValueError("The second argument must be a scalar.")
-
 # this has a different name, because _as_tensor is the function which ops use
 # to upcast their arguments... this internal-use function is a good place to put debugging stuff, better than the global astensor.
 _as_tensor = astensor
@@ -450,8 +415,6 @@ class Gemm(_Op):
         return ['<iostream>']
     def c_libraries(self):
         return blas.ldflags()
-    #def c_var_names(self):
-    #    return [['_z', '_a', '_x', '_y', '_b'], ['_zout']]
     def c_validate_update(self, *args):
         return ""
     def c_validate_update_cleanup(self, *args):
@@ -612,125 +575,3 @@ class Gemm(_Op):
         """ % dict(locals(), **sub)
 gemm = gof.op.constructor(Gemm)
 
-
-if 0:
-    ##########################
-    # Comparisons 
-    ##########################
-
-    # Less-than
-    class lt_elemwise(_Elemwise):
-        def __init__(self, *args):
-            raise NotImplementedError()
-    class lt_scalar_r(_Elemwise):
-        def __init__(self, *args):
-            raise NotImplementedError()
-    # Less-than or equal
-    class le_elemwise(_Elemwise):
-        def __init__(self, *args):
-            raise NotImplementedError()
-    class le_scalar_r(_Elemwise):
-        def __init__(self, *args):
-            raise NotImplementedError()
-    # Greater-than or equal
-    class gt_elemwise(_Elemwise):
-        def __init__(self, *args):
-            raise NotImplementedError()
-    class gt_scalar_r(_Elemwise):
-        def __init__(self, *args):
-            raise NotImplementedError()
-    # Greater-than or equal
-    class ge_elemwise(_Elemwise):
-        def __init__(self, *args):
-            raise NotImplementedError()
-    class ge_scalar_r(_Elemwise):
-        def __init__(self, *args):
-            raise NotImplementedError()
-
-
-
-
-if 0:
-    def _broadcastable_pattern(pattern):
-        def factory(data = None, name = None, dtype=None):
-            if data: 
-                assert len(data.shape) == len(pattern)
-                if dtype is not None:
-                    assert dtype is data.dtype
-                dtype = data.dtype
-                rval = Tensor(dtype, pattern, name)
-                rval.data = data
-            else:
-                rval = Tensor(dtype, pattern, name)
-            return  rval
-        return factory
-
-    row = _broadcastable_pattern([1, 0])
-    col = _broadcastable_pattern([0, 1])
-    matrix = _broadcastable_pattern([0, 0])
-
-if 0: #old __init__ code
-    """Create a Tensor
-
-    If data is given:
-        - constant defaults to True
-        - if dtype is given, it must match data.dtype
-            - otherwise: default is data.dtype
-        - if broadcastable is given, len(broadcastable) must match len(data.shape)
-            - otherwise: if it is constant, it defaults to 1 where shape[i]==1
-            - if it is not constant, it defaults to 0s
-
-    If data is not given:
-        - constant defaults to False
-    """
-    if dtype is None or broadcastable is None:
-        if data is None:
-            raise TypeError("Provide non-None data to complete the dtype and broadcastable flags.")
-        data = numpy.asarray(data)
-        if constant is None:
-            constant = True
-        dtype = data.dtype
-        if constant:
-            broadcastable = [1*(x == 1) for x in data.shape]
-        else:
-            broadcastable = [0] * len(data.shape)
-
-if 0:
-    def tensor__new__(cls, *args, **kwargs):
-        """__new__ is overloaded to handle the special form Tensor(x) when x is
-        a Tensor or an Op whose default output is a Tensor.  In these cases, the
-        argument x is returned, and a new Tensor is not created.
-        """
-        if len(args) == 1:
-            a = args[0]
-
-        t = super(Tensor, cls).__new__(cls, *args, **kwargs)
-        t.__init__(*args, **kwargs)
-        return t
-
-
-#         def upcast(dtype, *dtypes):
-#             z = numpy.zeros((), dtype = dtype)
-#             for dtype in dtypes:
-#                 z = z + numpy.zeros((), dtype = dtype)
-#             return str(z.dtype)
-#         for dtype in i_dtypes:
-#             if dtype is None:
-#                 raise TypeError("Expected a Tensor.")
-#         upcasted = upcast(*i_dtypes)
-#         return [upcasted] * self.nout
-# #         try:
-# #             dmap = self.destroy_map()
-# #         except AttributeError:
-# #             dmap = {}
-# #         rval = []
-# #         for i in xrange(self.nout):
-# #             if i in dmap:
-# #                 destroyed = dmap[output]
-# #                 if len(destroyed) != 1:
-# #                     raise TypeError("Cannot infer dtype of output %s because it destroys more than one input." % output)
-# #                 rval.append(destroyed[0])
-# #             else:
-# #                 rval.append(upcasted)
-# #         return rval
-