1 | // ----------------------------------------------------------------------- |
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2 | // interpolation.cc: Intepolate in or extrapolate from an array to |
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3 | // find values |
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4 | // ----------------------------------------------------------------------- |
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5 | // Copyright (C) 2006, Matthew Whiting, ATNF |
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6 | // |
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7 | // This program is free software; you can redistribute it and/or modify it |
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8 | // under the terms of the GNU General Public License as published by the |
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9 | // Free Software Foundation; either version 2 of the License, or (at your |
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10 | // option) any later version. |
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11 | // |
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12 | // Duchamp is distributed in the hope that it will be useful, but WITHOUT |
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13 | // ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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14 | // FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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15 | // for more details. |
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16 | // |
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17 | // You should have received a copy of the GNU General Public License |
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18 | // along with Duchamp; if not, write to the Free Software Foundation, |
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19 | // Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA |
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20 | // |
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21 | // Correspondence concerning Duchamp may be directed to: |
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22 | // Internet email: Matthew.Whiting [at] atnf.csiro.au |
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23 | // Postal address: Dr. Matthew Whiting |
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24 | // Australia Telescope National Facility, CSIRO |
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25 | // PO Box 76 |
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26 | // Epping NSW 1710 |
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27 | // AUSTRALIA |
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28 | // ----------------------------------------------------------------------- |
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29 | #include <iostream> |
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30 | #include <math.h> |
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31 | #include <duchamp/Utils/utils.hh> |
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32 | |
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33 | float interpolateToFindX(float yval, float *x, float *y, int size, int min, int max) |
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34 | { |
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35 | if(min<0) min=0; |
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36 | if(max<0) max=size-1; |
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37 | |
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38 | int i=min+1; |
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39 | bool foundIt=false; |
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40 | while( ((y[i]-yval)*(y[min]-yval) > 0) && i<max) i++; |
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41 | if(i==max){ |
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42 | if(y[min]>y[max]){ if(y[min]>yval) i=max; else i=min; } |
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43 | else{ if(y[min]>yval) i=min; else i=max; } |
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44 | } |
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45 | float slope = (y[i]-y[i-1])/(x[i]-x[i-1]); |
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46 | float xval = x[i-1] + (yval-y[i-1])/slope; |
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47 | return xval; |
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48 | } |
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49 | |
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50 | |
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51 | float interpolateToFindY(float xval, float *x, float *y, int size, int min, int max) |
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52 | { |
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53 | if(min<0) min=0; |
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54 | if(max<0) max=size; |
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55 | |
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56 | int i=min+1; |
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57 | while( ((x[i]-xval)*(x[i-1]-xval)>0) && i<max) i++; |
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58 | float slope = (y[i]-y[i-1])/(x[i]-x[i-1]); |
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59 | float yval = y[i-1] + (xval-x[i-1])*slope; |
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60 | return yval; |
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61 | } |
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