helpers: avoid mutation in invertible_matrices

Author: jakevdp

array_api_tests/hypothesis_helpers.py

@@ -1,5 +1,4 @@
 import re
-import itertools
 from contextlib import contextmanager
 from functools import reduce
 from math import sqrt
@@ -267,18 +266,14 @@ def invertible_matrices(draw, dtypes=xps.floating_dtypes(), stack_shapes=shapes(
     # For now, just generate stacks of diagonal matrices.
     n = draw(integers(0, SQRT_MAX_ARRAY_SIZE),)
     stack_shape = draw(stack_shapes)
-    shape = stack_shape + (n, n)
-    d = draw(xps.arrays(dtypes, shape=n*prod(stack_shape),
+    d = draw(xps.arrays(dtypes, shape=(*stack_shape, 1, n),
                         elements=dict(allow_nan=False, allow_infinity=False)))
     # Functions that require invertible matrices may do anything when it is
     # singular, including raising an exception, so we make sure the diagonals
     # are sufficiently nonzero to avoid any numerical issues.
     assume(xp.all(xp.abs(d) > 0.5))
-
-    a = xp.zeros(shape)
-    for j, (idx, i) in enumerate(itertools.product(sh.ndindex(stack_shape), range(n))):
-        a[idx + (i, i)] = d[j]
-    return a
+    diag_mask = xp.arange(n) == xp.arange(n)[:, None]
+    return xp.where(diag_mask, d, xp.zeros_like(d))
 
 # TODO: Better name
 @composite