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    "!="
        Not equal to.

            $A != $B;           # is $A not equal to $B?

    "neg"
        Negation.

            $B = -$A;           # $B is the negative of $A

    "~" Transpose.

            $B = ~$A;           # $B is the transpose of $A

    "abs"
        Absolute value.

            $B = abs $A;        # $B contains absolute values of $A

    "int"
        Truncate to integer.

            $B = int $A;        # $B contains only integers

IMPROVING THE SOLUTION OF LINEAR SYSTEMS
    The methods that do an explicit or implicit matrix left division accept
    some additional parameters. If these parameters are specified, the
    matrix left division is done repeatedly in an iterative way, which often
    gives a better solution.

  Background
    The linear system of equations

        $A * $x = $y

    can be solved for $x with

        $x = $y -> mldiv($A);

    Ideally "$A * $x" should equal $y, but due to numerical errors, this is
    not always the case. The following illustrates how to improve the
    solution $x computed above:

        $r = $A -> mmuladd($x, -$y);    # compute the residual $A*$x-$y
        $d = $r -> mldiv($A);           # compute the delta for $x
        $x -= $d;                       # improve the solution $x

    This procedure is repeated, and at each step, the absolute error

        ||$A*$x - $y|| = ||$r||

    and the relative error

        ||$A*$x - $y|| / ||$y|| = ||$r|| / ||$y||

    are computed and compared to the tolerances. Once one of the stopping
    criteria is satisfied, the algorithm terminates.

  Stopping criteria
    The algorithm stops when at least one of the errors are within the
    specified tolerances or the maximum number of iterations is reached. If
    the maximum number of iterations is reached, but noen of the errors are
    within the tolerances, a warning is displayed and the best solution so
    far is returned.

  Parameters
    MaxIter
        The maximum number of iterations to perform. The value must be a
        positive integer. The default is 20.

    RelTol
        The limit for the relative error. The value must be a non-negative.
        The default value is 1e-19 when perl is compiled with long doubles
        or quadruple precision, and 1e-9 otherwise.

    AbsTol
        The limit for the absolute error. The value must be a non-negative.
        The default value is 0.

    Debug
        If this parameter does not affect when the algorithm terminates, but
        when set to non-zero, some information is displayed at each step.

  Example
    If

        $A = [[  8, -8, -5,  6, -1,  3 ],
              [ -7, -1,  5, -9,  5,  6 ],
              [ -7,  8,  9, -2, -4,  3 ],
              [  3, -4,  5,  5,  3,  3 ],
              [  9,  8, -3, -4,  1,  6 ],
              [ -8,  9, -1,  3,  5,  2 ]];

        $y = [[  80, -13 ],
              [  -2, 104 ],
              [ -57, -27 ],
              [  47, -28 ],
              [   5,  77 ],
              [  91, 133 ]];

    the result of "$x = $y -> mldiv($A);", using double precision
    arithmetic, is the approximate solution

        $x = [[ -2.999999999999998, -5.000000000000000 ],
              [ -1.000000000000000,  3.000000000000001 ],
              [ -5.999999999999997, -8.999999999999996 ],
              [  8.000000000000000, -2.000000000000003 ],
              [  6.000000000000003,  9.000000000000002 ],
              [  7.999999999999997,  8.999999999999995 ]];

    The residual "$res = $A -> mmuladd($x, -$y);" is

        $res = [[  1.24344978758018e-14,  1.77635683940025e-15 ],
                [  8.88178419700125e-15, -5.32907051820075e-15 ],
                [ -1.24344978758018e-14,  1.77635683940025e-15 ],
                [ -7.10542735760100e-15, -4.08562073062058e-14 ],
                [ -1.77635683940025e-14, -3.81916720471054e-14 ],
                [  1.24344978758018e-14,  8.43769498715119e-15 ]];

    and the delta "$dx = $res -> mldiv($A);" is

        $dx = [[   -8.592098303124e-16, -2.86724066474914e-15 ],
               [ -7.92220125658508e-16, -2.99693950082398e-15 ],
               [ -2.22533360993874e-16,  3.03465504177947e-16 ],
               [  6.47376093198353e-17, -1.12378127899388e-15 ],
               [  6.35204502123966e-16,  2.40938179521241e-15 ],
               [  1.55166908001001e-15,  2.08339859425849e-15 ]];