Skip to content
Find file
Fetching contributors…
Cannot retrieve contributors at this time
203 lines (185 sloc) 6.12 KB
/*
* R : A Computer Language for Statistical Data Analysis
* Copyright (C) 1995-2012 The R Core Team
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, a copy is available at
* http://www.r-project.org/Licenses/
*/
/* Pretty Intervals
* ----------------
* Constructs m "pretty" values which cover the given interval *lo <= *up
* m ~= *ndiv + 1 (i.e., ndiv := approximate number of INTERVALS)
*
* It is not quite clear what should happen for *lo = *up;
* S itself behaves quite funilly, then.
*
* In my opinion, a proper 'pretty' should always ensure
* *lo < *up, and hence *ndiv >=1 in the result.
* However, in S and here, we allow *lo == *up, and *ndiv = 0.
* Note however, that we are NOT COMPATIBLE to S. [Martin M.]
*
* NEW (0.63.2): ns, nu are double (==> no danger of integer overflow)
*
* We determine
* if the interval (up - lo) is ``small'' [<==> i_small == TRUE, below].
* For the ``i_small'' situation, there is a parameter shrink_sml,
* the factor by which the "scale" is shrunk. ~~~~~~~~~~
* It is advisable to set it to some (smaller) integer power of 2,
* since this enables exact floating point division.
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#ifdef ENABLE_NLS
#include <libintl.h>
#define _(String) gettext (String)
#else
#define _(String) (String)
#endif
#include <math.h>
#include <float.h>
#include <R_ext/Applic.h>
#include <Rmath.h>
#include <R_ext/Error.h>
#ifdef DEBUGpr
# include <R_ext/Print.h>
#endif
#ifdef HAVE_VISIBILITY_ATTRIBUTE
# define attribute_hidden __attribute__ ((visibility ("hidden")))
#else
# define attribute_hidden
#endif
/* non-API, used by rgl */
double R_pretty0(double *lo, double *up, int *ndiv, int min_n,
double shrink_sml, double high_u_fact[],
int eps_correction, int return_bounds)
{
/* From version 0.65 on, we had rounding_eps := 1e-5, before, r..eps = 0
* 1e-7 is consistent with seq.default() */
#define rounding_eps 1e-7
#define h high_u_fact[0]
#define h5 high_u_fact[1]
double dx, cell, unit, base, U;
double ns, nu;
int k;
Rboolean i_small;
dx = *up - *lo;
/* cell := "scale" here */
if(dx == 0 && *up == 0) { /* up == lo == 0 */
cell = 1;
i_small = TRUE;
} else {
cell = fmax2(fabs(*lo),fabs(*up));
/* U = upper bound on cell/unit */
U = (1 + (h5 >= 1.5*h+.5)) ? 1/(1+h) : 1.5/(1+h5);
/* added times 3, as several calculations here */
i_small = dx < cell * U * imax2(1,*ndiv) * DBL_EPSILON *3;
}
/*OLD: cell = FLT_EPSILON+ dx / *ndiv; FLT_EPSILON = 1.192e-07 */
if(i_small) {
if(cell > 10)
cell = 9 + cell/10;
cell *= shrink_sml;
if(min_n > 1) cell /= min_n;
} else {
cell = dx;
if(*ndiv > 1) cell /= *ndiv;
}
if(cell < 20*DBL_MIN) {
warning(_("Internal(pretty()): very small range.. corrected"));
cell = 20*DBL_MIN;
} else if(cell * 10 > DBL_MAX) {
warning(_("Internal(pretty()): very large range.. corrected"));
cell = .1*DBL_MAX;
}
base = pow(10., floor(log10(cell))); /* base <= cell < 10*base */
/* unit : from { 1,2,5,10 } * base
* such that |u - cell| is small,
* favoring larger (if h > 1, else smaller) u values;
* favor '5' more than '2' if h5 > h (default h5 = .5 + 1.5 h) */
unit = base;
if((U = 2*base)-cell < h*(cell-unit)) { unit = U;
if((U = 5*base)-cell < h5*(cell-unit)) { unit = U;
if((U =10*base)-cell < h*(cell-unit)) unit = U; }}
/* Result: c := cell, u := unit, b := base
* c in [ 1, (2+ h) /(1+h) ] b ==> u= b
* c in ( (2+ h)/(1+h), (5+2h5)/(1+h5)] b ==> u= 2b
* c in ( (5+2h)/(1+h), (10+5h) /(1+h) ] b ==> u= 5b
* c in ((10+5h)/(1+h), 10 ) b ==> u=10b
*
* ===> 2/5 *(2+h)/(1+h) <= c/u <= (2+h)/(1+h) */
ns = floor(*lo/unit+rounding_eps);
nu = ceil (*up/unit-rounding_eps);
#ifdef DEBUGpr
REprintf("pretty(lo=%g,up=%g,ndiv=%d,min_n=%d,shrink=%g,high_u=(%g,%g),"
"eps=%d)\n\t dx=%g; is.small:%d. ==> cell=%g; unit=%g\n",
*lo, *up, *ndiv, min_n, shrink_sml, h, h5,
eps_correction, dx, (int)i_small, cell, unit);
#endif
if(eps_correction && (eps_correction > 1 || !i_small)) {
if(*lo) *lo *= (1- DBL_EPSILON); else *lo = -DBL_MIN;
if(*up) *up *= (1+ DBL_EPSILON); else *up = +DBL_MIN;
}
#ifdef DEBUGpr
if(ns*unit > *lo)
REprintf("\t ns= %.0f -- while(ns*unit > *lo) ns--;\n", ns);
#endif
while(ns*unit > *lo + rounding_eps*unit) ns--;
#ifdef DEBUGpr
if(nu*unit < *up)
REprintf("\t nu= %.0f -- while(nu*unit < *up) nu++;\n", nu);
#endif
while(nu*unit < *up - rounding_eps*unit) nu++;
k = (int)(0.5 + nu - ns);
if(k < min_n) {
/* ensure that nu - ns == min_n */
#ifdef DEBUGpr
REprintf("\tnu-ns=%.0f-%.0f=%d SMALL -> ensure nu-ns= min_n=%d\n",
nu,ns, k, min_n);
#endif
k = min_n - k;
if(ns >= 0.) {
nu += k/2;
ns -= k/2 + k%2;/* ==> nu-ns = old(nu-ns) + min_n -k = min_n */
} else {
ns -= k/2;
nu += k/2 + k%2;
}
*ndiv = min_n;
}
else {
*ndiv = k;
}
if(return_bounds) { /* if()'s to ensure that result covers original range */
if(ns * unit < *lo) *lo = ns * unit;
if(nu * unit > *up) *up = nu * unit;
} else {
*lo = ns;
*up = nu;
}
#ifdef DEBUGpr
REprintf("\t ns=%.0f ==> lo=%g\n", ns, *lo);
REprintf("\t nu=%.0f ==> up=%g ==> ndiv = %d\n", nu, *up, *ndiv);
#endif
return unit;
#undef h
#undef h5
}
attribute_hidden
void R_pretty(double *lo, double *up, int *ndiv, int *min_n,
double *shrink_sml, double *high_u_fact, int *eps_correction)
{
R_pretty0(lo, up, ndiv,
*min_n, *shrink_sml, high_u_fact, *eps_correction, 1);
}
Jump to Line
Something went wrong with that request. Please try again.