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/*
Grid.c
utility functions for the Vegas grid
this file is part of Suave
last modified 1 Jun 10 th
*/
static void RefineGrid(cThis *t, Grid grid, Grid margsum)
{
real avgperbin, thisbin, newcur, delta;
Grid imp, newgrid;
int bin, newbin;
/* smooth the f^2 value stored for each bin */
real prev = margsum[0];
real cur = margsum[1];
real norm = margsum[0] = .5*(prev + cur);
for( bin = 1; bin < NBINS - 1; ++bin ) {
creal s = prev + cur;
prev = cur;
cur = margsum[bin + 1];
norm += margsum[bin] = (s + cur)/3.;
}
norm += margsum[NBINS - 1] = .5*(prev + cur);
if( norm == 0 ) return;
norm = 1/norm;
/* compute the importance function for each bin */
avgperbin = 0;
for( bin = 0; bin < NBINS; ++bin ) {
real impfun = 0;
if( margsum[bin] > 0 ) {
creal r = margsum[bin]*norm;
avgperbin += impfun = pow((r - 1)/log(r), 1.5);
}
imp[bin] = impfun;
}
avgperbin /= NBINS;
/* redefine the size of each bin */
cur = newcur = 0;
thisbin = 0;
bin = -1;
for( newbin = 0; newbin < NBINS - 1; ++newbin ) {
while( thisbin < avgperbin ) {
thisbin += imp[++bin];
prev = cur;
cur = grid[bin];
}
thisbin -= avgperbin;
delta = (cur - prev)*thisbin;
newgrid[newbin] = SHARPEDGES ?
cur - delta/imp[bin] :
(newcur = Max(newcur + 0x1p-48,
cur - 2*delta/(imp[bin] + imp[IDim(bin - 1)])));
}
Copy(grid, newgrid, NBINS - 1);
grid[NBINS - 1] = 1;
}
/*********************************************************************/
static void Reweight(cThis *t, Bounds *b,
creal *w, creal *f, creal *lastf, cResult *total)
{
Grid margsum[NDIM];
real scale[NCOMP];
cbin_t *bin = (cbin_t *)lastf;
count dim, comp;
if( t->ncomp == 1 ) scale[0] = 1;
else {
for( comp = 0; comp < t->ncomp; ++comp )
scale[comp] = (total[comp].avg == 0) ? 0 : 1/total[comp].avg;
}
Zap(margsum);
while( f < lastf ) {
real fsq = 0;
for( comp = 0; comp < t->ncomp; ++comp )
fsq += Sq(*f++*scale[comp]);
fsq *= Sq(*w++);
if( fsq != 0 )
for( dim = 0; dim < t->ndim; ++dim )
margsum[dim][bin[dim]] += fsq;
bin += t->ndim;
}
for( dim = 0; dim < t->ndim; ++dim )
RefineGrid(t, b[dim].grid, margsum[dim]);
}
/*********************************************************************/
static void StretchGrid(cGrid grid, Grid gridL, Grid gridR)
{
real prev = 0, cur, step, x;
count bin = 0;
while( bin < NBINS ) {
cur = grid[bin++];
if( cur >= .5 ) break;
prev = cur;
}
step = (bin - (cur - .5)/(cur - prev))/NBINS;
prev = x = 0;
cur = *grid;
for( bin = 0; bin < NBINS; ++bin ) {
x += step;
if( x > 1 ) {
--x;
prev = cur;
cur = *++grid;
}
gridL[bin] = 2*(prev + (cur - prev)*x);
}
step = 1 - step;
for( bin = 0; bin < NBINS - 1; ++bin ) {
x += step;
if( x > 1 ) {
--x;
prev = cur;
cur = *++grid;
}
gridR[bin] = 2*(prev + (cur - prev)*x) - 1;
}
gridR[NBINS - 1] = 1;
}
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