tron.cpp

Go to the documentation of this file.

#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdarg.h>

#include <shogun/lib/config.h>
#include <shogun/lib/Signal.h>
#include <shogun/lib/Time.h>

#ifdef HAVE_LAPACK
#include <shogun/mathematics/lapack.h>
#include <shogun/mathematics/Math.h>
#include <shogun/optimization/liblinear/tron.h>

using namespace shogun;

CTron::CTron(const function *f, float64_t e, int32_t it)
: CSGObject()
{
    this->fun_obj=const_cast<function *>(f);
    this->eps=e;
    this->max_iter=it;
}

CTron::~CTron()
{
}

void CTron::tron(float64_t *w, float64_t max_train_time)
{
    // Parameters for updating the iterates.
    float64_t eta0 = 1e-4, eta1 = 0.25, eta2 = 0.75;

    // Parameters for updating the trust region size delta.
    float64_t sigma1 = 0.25, sigma2 = 0.5, sigma3 = 4.;

    int32_t i, cg_iter;
    float64_t delta, snorm, one=1.0;
    float64_t alpha, f, fnew, prered, actred, gs;

    /* calling external lib */
    int n = (int) fun_obj->get_nr_variable();
    int search = 1, iter = 1, inc = 1;
    double *s = SG_MALLOC(double, n);
    double *r = SG_MALLOC(double, n);
    double *w_new = SG_MALLOC(double, n);
    double *g = SG_MALLOC(double, n);

    for (i=0; i<n; i++)
        w[i] = 0;

    f = fun_obj->fun(w);
    fun_obj->grad(w, g);
    delta = cblas_dnrm2(n, g, inc);
    float64_t gnorm1 = delta;
    float64_t gnorm = gnorm1;

    if (gnorm <= eps*gnorm1)
        search = 0;

    iter = 1;

    CSignal::clear_cancel();
    CTime start_time;

    while (iter <= max_iter && search && (!CSignal::cancel_computations()))
    {
        if (max_train_time > 0 && start_time.cur_time_diff() > max_train_time)
          break;

        cg_iter = trcg(delta, g, s, r);

        memcpy(w_new, w, sizeof(float64_t)*n);
        cblas_daxpy(n, one, s, inc, w_new, inc);

        gs = cblas_ddot(n, g, inc, s, inc);
        prered = -0.5*(gs-cblas_ddot(n, s, inc, r, inc));
            fnew = fun_obj->fun(w_new);

        // Compute the actual reduction.
            actred = f - fnew;

        // On the first iteration, adjust the initial step bound.
        snorm = cblas_dnrm2(n, s, inc);
        if (iter == 1)
            delta = CMath::min(delta, snorm);

        // Compute prediction alpha*snorm of the step.
        if (fnew - f - gs <= 0)
            alpha = sigma3;
        else
            alpha = CMath::max(sigma1, -0.5*(gs/(fnew - f - gs)));

        // Update the trust region bound according to the ratio of actual to predicted reduction.
        if (actred < eta0*prered)
            delta = CMath::min(CMath::max(alpha, sigma1)*snorm, sigma2*delta);
        else if (actred < eta1*prered)
            delta = CMath::max(sigma1*delta, CMath::min(alpha*snorm, sigma2*delta));
        else if (actred < eta2*prered)
            delta = CMath::max(sigma1*delta, CMath::min(alpha*snorm, sigma3*delta));
        else
            delta = CMath::max(delta, CMath::min(alpha*snorm, sigma3*delta));

        SG_INFO("iter %2d act %5.3e pre %5.3e delta %5.3e f %5.3e |g| %5.3e CG %3d\n", iter, actred, prered, delta, f, gnorm, cg_iter);

        if (actred > eta0*prered)
        {
            iter++;
            memcpy(w, w_new, sizeof(float64_t)*n);
            f = fnew;
                fun_obj->grad(w, g);

            gnorm = cblas_dnrm2(n, g, inc);
            if (gnorm < eps*gnorm1)
                break;
            SG_SABS_PROGRESS(gnorm, -CMath::log10(gnorm), -CMath::log10(1), -CMath::log10(eps*gnorm1), 6);
        }
        if (f < -1.0e+32)
        {
            SG_WARNING("f < -1.0e+32\n");
            break;
        }
        if (CMath::abs(actred) <= 0 && CMath::abs(prered) <= 0)
        {
            SG_WARNING("actred and prered <= 0\n");
            break;
        }
        if (CMath::abs(actred) <= 1.0e-12*CMath::abs(f) &&
            CMath::abs(prered) <= 1.0e-12*CMath::abs(f))
        {
            SG_WARNING("actred and prered too small\n");
            break;
        }
    }

    SG_DONE();

    SG_FREE(g);
    SG_FREE(r);
    SG_FREE(w_new);
    SG_FREE(s);
}

int32_t CTron::trcg(float64_t delta, double* g, double* s, double* r)
{
    /* calling external lib */
    int i, cg_iter;
    int n = (int) fun_obj->get_nr_variable();
    int inc = 1;
    double one = 1;
    double *Hd = SG_MALLOC(double, n);
    double *d = SG_MALLOC(double, n);
    double rTr, rnewTrnew, alpha, beta, cgtol;

    for (i=0; i<n; i++)
    {
        s[i] = 0;
        r[i] = -g[i];
        d[i] = r[i];
    }
    cgtol = 0.1* cblas_dnrm2(n, g, inc);

    cg_iter = 0;
    rTr = cblas_ddot(n, r, inc, r, inc);
    while (1)
    {
        if (cblas_dnrm2(n, r, inc) <= cgtol)
            break;
        cg_iter++;
        fun_obj->Hv(d, Hd);

        alpha = rTr/cblas_ddot(n, d, inc, Hd, inc);
        cblas_daxpy(n, alpha, d, inc, s, inc);
        if (cblas_dnrm2(n, s, inc) > delta)
        {
            SG_INFO("cg reaches trust region boundary\n");
            alpha = -alpha;
            cblas_daxpy(n, alpha, d, inc, s, inc);

            double std = cblas_ddot(n, s, inc, d, inc);
            double sts = cblas_ddot(n, s, inc, s, inc);
            double dtd = cblas_ddot(n, d, inc, d, inc);
            double dsq = delta*delta;
            double rad = sqrt(std*std + dtd*(dsq-sts));
            if (std >= 0)
                alpha = (dsq - sts)/(std + rad);
            else
                alpha = (rad - std)/dtd;
            cblas_daxpy(n, alpha, d, inc, s, inc);
            alpha = -alpha;
            cblas_daxpy(n, alpha, Hd, inc, r, inc);
            break;
        }
        alpha = -alpha;
        cblas_daxpy(n, alpha, Hd, inc, r, inc);
        rnewTrnew = cblas_ddot(n, r, inc, r, inc);
        beta = rnewTrnew/rTr;
        cblas_dscal(n, beta, d, inc);
        cblas_daxpy(n, one, r, inc, d, inc);
        rTr = rnewTrnew;
    }

    SG_FREE(d);
    SG_FREE(Hd);

    return(cg_iter);
}

float64_t CTron::norm_inf(int32_t n, float64_t *x)
{
    float64_t dmax = CMath::abs(x[0]);
    for (int32_t i=1; i<n; i++)
        if (CMath::abs(x[i]) >= dmax)
            dmax = CMath::abs(x[i]);
    return(dmax);
}
#endif //HAVE_LAPACK