!12530 add meshgrid support for start <= stop & complex step with real component

From: @jachua
Reviewed-by: @guoqi1024,@liangchenghui
Signed-off-by: @liangchenghui

mindspore/numpy/array_creations.py

@@ -1291,6 +1291,12 @@ def meshgrid(*xi, sparse=False, indexing='xy'):
     if indexing not in ('xy', 'ij'):
         _raise_type_error("Valid values for `indexing` are 'xy' and 'ij'.")
 
+    shape_out = ()
+    for x in xi:
+        shape_out += (x.size,)
+    if _is_shape_empty(shape_out):
+        return ones(shape_out)
+
     grids = []
     for x in xi:
         if F.rank(x) == 1:
@@ -1351,7 +1357,7 @@ class nd_grid:
             else:
                 step = 1
             if isinstance(step, complex):
-                v = linspace(k.start, k.stop, int(abs(step.imag)))
+                v = linspace(k.start, k.stop, int(abs(step)))
             else:
                 v = arange(k.start, k.stop, step)
             xi.append(v)
@@ -1362,6 +1368,8 @@ class nd_grid:
         if self.sparse:
             return grids
 
+        if isinstance(grids, Tensor_):
+            return grids
         expanded = []
         for grid in grids:
             expanded.append(F.expand_dims(grid, 0))
@@ -1380,6 +1388,11 @@ class mGridClass(nd_grid):
     as specifying the number of points to create between the start and
     stop values, where the stop value is inclusive.
 
+    Note:
+        Unlike Numpy, if the step length is a complex number with a real
+        component, the step length is handled as equivalent to
+        ``int(abs(step))``.
+
     Returns:
         Tensor or tuple of tensor, a meshgrid.
 
@@ -1422,6 +1435,11 @@ class oGridClass(nd_grid):
     as specifying the number of points to create between the start and
     stop values, where the stop value is inclusive.
 
+    Note:
+        Unlike Numpy, if the step length is a complex number with a real
+        component, the step length is handled as equivalent to
+        ``int(abs(step))``.
+
     Raises:
         TypeError: if slicing indices are not integers.