Fix of matrix_format (#843)

Closes #840 

This fixes an ugly bug that produced non-sense text representations of
the covariance matrix. The numerical values in the matrix were correct,
but the text representation, which aims to make the numbers look
reasonable for humans, produced a completely wrong result, see #840 for
how badly that failed.

To make things worse, this wrong behavior was actually accepted by a
unit test, which expected the wrong outcome 🤦

Author: HDembinski

src/iminuit/_repr_html.py

@@ -283,7 +283,7 @@ def matrix(arr):
 
     n = len(names)
 
-    nums = matrix_format(arr.flatten())
+    nums = matrix_format(arr)
 
     grad = ColorGradient(
         (-1.0, 120.0, 120.0, 250.0),

src/iminuit/_repr_text.py

@@ -180,7 +180,7 @@ def matrix(arr):
     names = tuple(arr._var2pos)
 
     n = len(arr)
-    nums = matrix_format(arr.flatten())
+    nums = matrix_format(arr)
 
     def row_fmt(args):
         s = "│ " + args[0] + " │"
@@ -209,6 +209,13 @@ def row_fmt(args):
     return "\n".join(lines)
 
 
-def matrix_format(values):
-    s = [f"{v:.3g}" % v for v in values]
-    return _strip(s)
+def matrix_format(matrix):
+    r = []
+    for i in range(matrix.shape[0]):
+        for j in range(matrix.shape[1]):
+            if i == j:
+                r.append(f"{matrix[i, i]:.3g}")
+            else:
+                x = pdg_format(matrix[i, j], matrix[i, i], matrix[j, j])[0]
+                r.append(x)
+    return r

src/iminuit/pdg_format.py

@@ -159,6 +159,7 @@ def pdg_format(value, error, *errors, labels=None, format=term, leader=None, exp
 
 
 def _strip(items: List[str]) -> List[str]:
+    assert all("e" not in x for x in items)
     # ignore inf and nan
     mask = tuple(i for (i, s) in enumerate(items) if "." in s)
     if mask:

src/iminuit/util.py

@@ -289,16 +289,9 @@ def __array_finalize__(self, obj: Any) -> None:
         else:
             self._var2pos = getattr(obj, "_var2pos", {})
 
-    def __getitem__(  # type:ignore # mypy complains about incompatible signatures
+    def __getitem__(  # type:ignore
         self,
-        key: Union[
-            int,
-            str,
-            Tuple[Union[int, str], Union[int, str]],
-            Iterable[Union[int, str]],
-            NDArray,
-            slice,
-        ],
+        key: Union[Key, Tuple[Key, Key], Iterable[Key], NDArray],
     ) -> NDArray:
         """Get matrix element at key."""
         var2pos = self._var2pos
@@ -358,7 +351,7 @@ def to_table(self) -> Tuple[List[List[str]], Tuple[str, ...]]:
         y    -0    4
         """
         names = tuple(self._var2pos)  # type:ignore
-        nums = _repr_text.matrix_format(self.flatten())  # type:ignore
+        nums = _repr_text.matrix_format(self)
         tab = []
         n = len(self)
         for i, name in enumerate(names):

tests/matrix.html

@@ -7,11 +7,11 @@
     <tr>
         <th> x </th>
         <td> 1 </td>
-        <td style="background-color:rgb(250,250,250);color:black"> 0 </td>
+        <td style="background-color:rgb(250,250,250);color:black"> 0.00 </td>
     </tr>
     <tr>
         <th> y </th>
-        <td style="background-color:rgb(250,250,250);color:black"> 0 </td>
+        <td style="background-color:rgb(250,250,250);color:black"> 0.00 </td>
         <td> 0.25 </td>
     </tr>
 </table>

tests/matrix.txt

@@ -1,6 +1,6 @@
-┌───┬───────────┐
-│   │    x    y │
-├───┼───────────┤
-│ x │    1   -0 │
-│ y │   -0 0.25 │
-└───┴───────────┘
+┌───┬─────────────┐
+│   │     x     y │
+├───┼─────────────┤
+│ x │     1 -0.00 │
+│ y │ -0.00  0.25 │
+└───┴─────────────┘

tests/matrix_2.html

@@ -7,11 +7,11 @@
     <tr>
         <th> x </th>
         <td> 1 </td>
-        <td style="background-color:rgb(250,144,144);color:black"> 0.707 </td>
+        <td style="background-color:rgb(250,144,144);color:black"> 0.7 </td>
     </tr>
     <tr>
         <th> y </th>
-        <td style="background-color:rgb(250,144,144);color:black"> 0.707 </td>
+        <td style="background-color:rgb(250,144,144);color:black"> 0.7 </td>
         <td> 1 </td>
     </tr>
 </table>

tests/matrix_difficult_values.txt

@@ -1,6 +1,6 @@
 ┌───┬─────────────┐
 │   │     x     y │
 ├───┼─────────────┤
-│ x │ -1.23     0 │
-│ y │     0     0 │
+│ x │ -1.23   0.0 │
+│ y │   0.0     0 │
 └───┴─────────────┘

tests/test_repr.py

@@ -80,23 +80,23 @@ def test_pdg_format():
 
 def test_matrix_format():
     def a(*args):
-        return np.array(args)
+        return np.reshape(args, (2, 2))
 
     assert _repr_text.matrix_format(a(1e1, 2e2, -3e3, -4e4)) == [
         "10",
         "200",
-        "-3e+03",
+        "-3.00e3",
         "-4e+04",
     ]
-    assert _repr_text.matrix_format(a(nan, 2e2, -nan, -4e4)) == [
-        "nan",
+    assert _repr_text.matrix_format(a(2e2, nan, -nan, -4e4)) == [
         "200",
         "nan",
+        "nan",
         "-4e+04",
     ]
-    assert _repr_text.matrix_format(a(inf, 2e2, -nan, -4e4)) == [
-        "inf",
+    assert _repr_text.matrix_format(a(2e2, inf, -nan, -4e4)) == [
         "200",
+        "inf",
         "nan",
         "-4e+04",
     ]

tests/test_tabulate.py

@@ -31,9 +31,9 @@ def test_matrix():
     assert (
         framed(tab.tabulate(*m.covariance.to_table()))
         == """
-         x       y
---  ------  ------
-x    1      -0.643
-y   -0.643   4
+      x    y
+--  ---  ---
+x     1   -0
+y    -0    4
 """
     )