Page Menu
Home
c4science
Search
Configure Global Search
Log In
Files
F78712169
mgpt_splinetab.cpp
No One
Temporary
Actions
Download File
Edit File
Delete File
View Transforms
Subscribe
Mute Notifications
Award Token
Subscribers
None
File Metadata
Details
File Info
Storage
Attached
Created
Thu, Aug 22, 13:32
Size
3 KB
Mime Type
text/x-c
Expires
Sat, Aug 24, 13:32 (2 d)
Engine
blob
Format
Raw Data
Handle
20035358
Attached To
rLAMMPS lammps
mgpt_splinetab.cpp
View Options
/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
http://lammps.sandia.gov, Sandia National Laboratories
Steve Plimpton, sjplimp@sandia.gov
Copyright (2003) Sandia Corporation. Under the terms of Contract
DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
certain rights in this software. This software is distributed under
the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
This file is part of the MGPT implementation. See further comments
in pair_mgpt.cpp and pair_mgpt.h.
------------------------------------------------------------------------- */
#include "mgpt_splinetab.h"
static void trisolve(int n,double A[][3],double y[]) {
/* Backward elimination */
for(int i = n-1; i>0; i--) {
double q = A[i-1][2] / A[i][1];
A[i-1][1] = A[i-1][1] - q*A[i][0];
y[i-1] = y[i-1] - q*y[i];
}
/* Forward substitution */
y[0] = y[0] / A[0][1];
for(int i = 1; i<n; i++)
y[i] = (y[i] - A[i][0]*y[i-1]) / A[i][1];
}
void makespline(int ntab,int stride,double tab[],double C[][4]) {
int n = 3*(ntab-1);
double (*A)[3] = new double[n][3];
double *y = new double[n];
double h_left,h_right,d;
int i,j;
/* Second order second derivative approximation
at end points. */
h_left =
2.0*tab[stride*0] - 5.0*tab[stride*1] +
4.0*tab[stride*2] - 1.0*tab[stride*3];
h_right =
2.0*tab[stride*(ntab-1)] - 5.0*tab[stride*(ntab-2)] +
4.0*tab[stride*(ntab-3)] - 1.0*tab[stride*(ntab-4)];
A[0][0] = 0.0; A[0][1] = 0.0; A[0][2] = 2.0; y[0] = h_left;
for(i = 1; i<ntab-1; i++) {
j = 3*(i-1);
d = tab[stride*i] - tab[stride*(i-1)];
A[j+1][0] = 1.0; A[j+1][1] = 1.0; A[j+1][2] = 1.0; y[j+1] = d;
A[j+2][0] = 1.0; A[j+2][1] = 2.0; A[j+2][2] = -1.0; y[j+2] = -d;
A[j+3][0] = 2.0; A[j+3][1] = 2.0; A[j+3][2] = -2.0; y[j+3] = 2.0*d;
}
j = 3*(ntab-2);
d = tab[stride*(ntab-1)] - tab[stride*(ntab-2)];
A[j+1][0] = 1.0; A[j+1][1] = 1.0; A[j+1][2] = 1.0; y[j+1] = d;
A[j+2][0] = 2.0; A[j+2][1] = 6.0; A[j+2][2] = 0.0; y[j+2] = h_right;
trisolve(n,A,y);
for(i = 0; i<ntab-1; i++) {
C[i][0] = tab[stride*i];
C[i][1] = y[3*i+0];
C[i][2] = y[3*i+1];
C[i][3] = y[3*i+2];
}
delete[] y;
delete[] A;
}
void evalcubic(double p[4],double x,double *y,double *dy,double *d2y) {
double t1,t2,t3;
t1 = p[2] + x*p[3];
t2 = p[1] + x*t1;
t3 = t1 + x*p[3];
*y = p[0] + x*t2;
*dy = (t2 + x*t3);
*d2y = 2.0*(t3 + x*p[3]);
}
void evalspline(int n,double x0,double x1,double C[][4],
double x,double *y,double *dy,double *d2y) {
double xhat,t1,t2,t3;
double *p;
int idx;
double dxinv = n/(x1-x0);
xhat = (x-x0)/(x1-x0) * n;
idx = (int) xhat;
if(idx < 0) idx = 0;
if(idx > n-1) idx = n-1;
xhat = xhat - idx;
p = C[idx];
if(0) {
*y = p[0] + xhat*(p[1] + xhat*(p[2] + xhat*p[3]));
*dy = p[1] + xhat*(2*p[2] + xhat*3*p[3]);
*d2y = 2*p[2] + xhat*6*p[3];
*dy *= dxinv;
*d2y *= dxinv*dxinv;
} else {
t1 = p[2] + xhat*p[3];
t2 = p[1] + xhat*t1;
t3 = t1 + xhat*p[3];
*y = p[0] + xhat*t2;
*dy = (t2 + xhat*t3)*dxinv;
*d2y = 2.0*(t3 + xhat*p[3])*(dxinv*dxinv);
}
}
Event Timeline
Log In to Comment