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chrisfen |
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************************************************************************** |
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S2kit 1.0 |
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A lite version of Spherical Harmonic Transform Kit |
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Peter Kostelec, Dan Rockmore |
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{geelong,rockmore}@cs.dartmouth.edu |
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Contact: Peter Kostelec |
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geelong@cs.dartmouth.edu |
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Copyright 2004 Peter Kostelec, Dan Rockmore |
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This file is part of S2kit. |
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S2kit is free software; you can redistribute it and/or modify |
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it under the terms of the GNU General Public License as published by |
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the Free Software Foundation; either version 2 of the License, or |
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(at your option) any later version. |
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S2kit is distributed in the hope that it will be useful, |
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but WITHOUT ANY WARRANTY; without even the implied warranty of |
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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GNU General Public License for more details. |
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You should have received a copy of the GNU General Public License |
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along with S2kit; if not, write to the Free Software |
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
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See the accompanying LICENSE file for details. |
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************************************************************************ |
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************************************************************************/ |
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/* |
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some "primitive" functions that are used in cospmls.c |
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and newmathx.c |
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*/ |
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#include <math.h> |
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#include <string.h> /* to declare memcpy */ |
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#ifndef PI |
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#define PI 3.14159265358979 |
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#endif |
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/************************************************************************/ |
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/* Recurrence coefficients */ |
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/************************************************************************/ |
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/* Recurrence coefficents for L2-normed associated Legendre |
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recurrence. When using these coeffs, make sure that |
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inital Pmm function is also L2-normed */ |
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/* l represents degree, m is the order */ |
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double L2_an(int m, |
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int l) |
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{ |
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return (sqrt((((double) (2*l+3))/((double) (2*l+1))) * |
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(((double) (l-m+1))/((double) (l+m+1)))) * |
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(((double) (2*l+1))/((double) (l-m+1)))); |
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} |
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/* note - if input l is zero, need to return 0 */ |
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double L2_cn(int m, |
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int l) |
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{ |
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if (l != 0) { |
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return (-1.0 * |
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sqrt((((double) (2*l+3))/((double) (2*l-1))) * |
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(((double) (l-m+1))/((double) (l+m+1))) * |
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(((double) (l-m))/((double) (l+m)))) * |
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(((double) (l+m))/((double) (l-m+1)))); |
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} |
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else |
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return 0.0; |
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} |
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/* when using the reverse recurrence, instead of calling |
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1/L2_cn_tr(m,l), let me just define the function ... |
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it might be more stable */ |
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double L2_cn_inv(int m, |
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int l) |
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{ |
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double dl, dm; |
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dl = (double) l; |
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dm = (double) m; |
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return ( -(1.0 + (1. - 2. * dm)/(dm + dl)) * |
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sqrt( ((-1. + 2.*dl)/(3. + 2.*dl)) * |
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((dl + dl*dl + dm + 2.*dl*dm + dm*dm)/ |
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(dl + dl*dl - dm - 2.*dl*dm + dm*dm)) ) |
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); |
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} |
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/* when using the reverse recurrence, instead of calling |
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-L2_an(m,l)/L2_cn(m,l), let me just define the |
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function ... it might be more stable */ |
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double L2_ancn(int m, |
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int l) |
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{ |
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double dl, dm; |
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dl = (double) l; |
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dm = (double) m; |
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return( sqrt( 4.0 + ( (4.0 * dm * dm - 1.0)/ |
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(dl * dl - dm * dm) ) ) ); |
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} |
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/************************************************************************/ |
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/* vector arithmetic operations */ |
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/************************************************************************/ |
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/* does result = data1 + data2 */ |
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/* result and data are vectors of length n */ |
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void vec_add(double *data1, |
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double *data2, |
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double *result, |
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int n) |
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{ |
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int k; |
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for (k = 0; k < n % 4; ++k) |
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result[k] = data1[k] + data2[k]; |
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for ( ; k < n ; k += 4) |
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{ |
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result[k] = data1[k] + data2[k]; |
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result[k + 1] = data1[k + 1] + data2[k + 1]; |
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result[k + 2] = data1[k + 2] + data2[k + 2]; |
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result[k + 3] = data1[k + 3] + data2[k + 3]; |
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} |
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} |
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/************************************************************************/ |
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/************************************************************************/ |
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/* |
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vec_mul(scalar,data1,result,n) multiplies the vector 'data1' by |
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'scalar' and returns in result |
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*/ |
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void vec_mul(double scalar, |
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double *data1, |
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double *result, |
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int n) |
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{ |
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int k; |
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for( k = 0; k < n % 4; ++k) |
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result[k] = scalar * data1[k]; |
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for( ; k < n; k +=4) |
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{ |
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result[k] = scalar * data1[k]; |
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result[k + 1] = scalar * data1[k + 1]; |
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result[k + 2] = scalar * data1[k + 2]; |
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result[k + 3] = scalar * data1[k + 3]; |
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} |
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} |
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/************************************************************************/ |
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/* point-by-point multiplication of vectors */ |
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void vec_pt_mul(double *data1, |
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double *data2, |
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double *result, |
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int n) |
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{ |
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int k; |
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for(k = 0; k < n % 4; ++k) |
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result[k] = data1[k] * data2[k]; |
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for( ; k < n; k +=4) |
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{ |
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result[k] = data1[k] * data2[k]; |
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result[k + 1] = data1[k + 1] * data2[k + 1]; |
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result[k + 2] = data1[k + 2] * data2[k + 2]; |
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result[k + 3] = data1[k + 3] * data2[k + 3]; |
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} |
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} |
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/************************************************************************/ |
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/* returns an array of the angular arguments of n Chebyshev nodes */ |
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/* eval_pts points to a double array of length n */ |
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void ArcCosEvalPts(int n, |
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double *eval_pts) |
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{ |
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int i; |
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double twoN; |
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twoN = (double) (2 * n); |
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for (i=0; i<n; i++) |
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eval_pts[i] = (( 2.0*((double)i)+1.0 ) * PI) / twoN; |
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} |
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/************************************************************************/ |
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/* returns an array of n Chebyshev nodes */ |
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void EvalPts( int n, |
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double *eval_pts) |
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{ |
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int i; |
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double twoN; |
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twoN = (double) (2*n); |
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for (i=0; i<n; i++) |
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eval_pts[i] = cos((( 2.0*((double)i)+1.0 ) * PI) / twoN); |
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} |
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/************************************************************************/ |
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/* L2 normed Pmm. Expects input to be the order m, an array of |
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evaluation points arguments of length n, and a result vector of length n */ |
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/* The norming constant can be found in Sean's PhD thesis */ |
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/* This has been tested and stably computes Pmm functions thru bw=512 */ |
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void Pmm_L2( int m, |
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double *eval_pts, |
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int n, |
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double *result) |
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{ |
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int i; |
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double md, id, mcons; |
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id = (double) 0.0; |
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md = (double) m; |
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mcons = sqrt(md + 0.5); |
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for (i=0; i<m; i++) { |
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mcons *= sqrt((md-(id/2.0))/(md-id)); |
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id += 1.0; |
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} |
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if (m != 0 ) |
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mcons *= pow(2.0,-md/2.0); |
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if ((m % 2) != 0) mcons *= -1.0; |
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for (i=0; i<n; i++) |
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result[i] = mcons * pow(sin(eval_pts[i]),((double) m)); |
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} |
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/************************************************************************/ |
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/************************************************************************/ |
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/* |
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This piece of code synthesizes a function which is the weighted sum of |
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L2-normalized associated Legendre functions. |
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The coeffs array should contain bw - m coefficients ordered from |
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zeroth degree to bw-1, and eval_pts should be an array of the |
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arguments (arccos) of the desired evaluation points of length 2*bw. |
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Answer placed in result (and has length 2*bw). |
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workspace needs to be of size 16 * bw |
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*/ |
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void P_eval(int m, |
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double *coeffs, |
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double *eval_args, |
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double *result, |
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double *workspace, |
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int bw) |
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{ |
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double *prev, *prevprev, *temp1, *temp2, *temp3, *temp4, *x_i; |
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int i, j, n; |
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double splat; |
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prevprev = workspace; |
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prev = prevprev + (2*bw); |
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temp1 = prev + (2*bw); |
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temp2 = temp1 + (2*bw); |
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temp3 = temp2 + (2*bw); |
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temp4 = temp3 + (2*bw); |
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x_i = temp4 + (2*bw); |
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n = 2*bw; |
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/* now get the evaluation nodes */ |
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EvalPts(n,x_i); |
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/* for(i=0;i<n;i++) |
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fprintf(stderr,"in P_eval evalpts[%d] = %lf\n", i, x_i[i]); |
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*/ |
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for (i=0; i<n; i++) |
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prevprev[i] = 0.0; |
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if (m == 0) { |
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for (i=0; i<n; i++) { |
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prev[i] = 0.707106781186547; /* sqrt(1/2) */ |
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/* now mult by first coeff and add to result */ |
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result[i] = coeffs[0] * prev[i]; |
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} |
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} |
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else { |
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Pmm_L2(m, eval_args, n, prev); |
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splat = coeffs[0]; |
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for (i=0; i<n; i++) |
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result[i] = splat * prev[i]; |
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} |
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for (i=0; i<bw-m-1; i++) { |
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vec_mul(L2_cn(m,m+i),prevprev,temp1,n); |
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vec_pt_mul(prev, x_i, temp2, n); |
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vec_mul(L2_an(m,m+i), temp2, temp3, n); |
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vec_add(temp3, temp1, temp4, n); /* temp4 now contains P(m,m+i+1) */ |
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/* now add weighted P(m,m+i+1) to the result */ |
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splat = coeffs[i+1]; |
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for (j=0; j<n; j++) |
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result[j] += splat * temp4[j]; |
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memcpy(prevprev, prev, sizeof(double) * n); |
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memcpy(prev, temp4, sizeof(double) * n); |
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} |
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} |
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