[Octave-bug-tracker] [bug #37414] Some minor bugs in quadcc

[Pedro Gonnet]

Follow-up Comment #2, bug #37414 (project octave):

Hi Rik,

Sure, here's an example of integrating a function, in this case sin(x), that
has random occurrences of 'NaN' in it:

    function y = mysin ( x )
        y = sin(x);
        ind = ceil( rand(1) * size(y) );
        y(ind) = NaN;
    end

Integrating the non-faulty function from -pi to pi gives, as expected, zero:

    octave:2> [ q , err , npoints ] = quadcc( @sin , -pi , pi )
    q = -2.8189e-17
    err =  7.3915e-16
    npoints =  95

Integrating the faulty function in the same interval does not converge at
all:

    octave:5> [ q , err , npoints ] = quadcc( @mysin , -pi , pi )
    q = -0.026062
    err =  2.1504
    npoints =  167589

However, with the code fixes (fixed and re-compiled), the integrator gets to
within 13 digits of the correct result:

    octave:3> [ q , err , npoints ] = quadcc( @mysin , -pi , pi )
    q =  3.7813e-14
    err =  6.1902e-12
    npoints =  198919

Incidentally, this is a nice example of the robustness of this code, at least
in the corrected version, for an integrand at which all other codes fail :)


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