Mathematics Upgrade Issues :: MATLAB 6.5 Release Notes (MATLAB Release Notes)

MATLAB Release Notes

Mathematics Upgrade Issues

The issues involved in upgrading from MATLAB 6.1 to MATLAB 6.5, in terms of mathematics features, are discussed below.

Singular Triangular Matrix Division

The result of dividing a singular lower or upper triangular matrix by any other matrix, using either left (\) or right (/) division may change. Previously, for singular square matrices A for which rcond(A) = 0, the result was always a matrix of Infs.

This change is a result of performance improvements described in Mathematics Features.

Example 1.

In MATLAB Version 6.5,

A = [1 2 3;0 4 5;0 0 0];
b = [1;2;3];
A\b
Warning: Matrix is close to singular or badly scaled.
         Results may be inaccurate. RCOND = 0.000000e+000.

ans =
   NaN
  -Inf
   Inf

Previously, the result was

```
[Inf
 Inf
 Inf]
```

Example 2.

In MATLAB 6.5, a zero matrix is treated as a singular triangular matrix.

[0 0;0 0] \ [0 0]'
Warning: Matrix is close to singular or badly scaled.
         Results may be inaccurate. RCOND = 0.000000e+000.

ans =
   NaN
   NaN

Previously the result was

```
[Inf
 Inf]
```

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