1 | ;------------------------------------------------------------ |
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2 | ;------------------------------------------------------------ |
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3 | ;------------------------------------------------------------ |
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4 | ;+ |
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5 | ; |
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6 | ; @file_comments |
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7 | ; calculate the different elements of 2 matrix of positive whole numbers. |
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8 | ; |
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9 | ; @categories |
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10 | ; Calculation |
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11 | ; |
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12 | ; @param a {in}{required} arrays of positive integers, which need |
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13 | ; not be sorted. Duplicate elements are ignored, as they have no |
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14 | ; effect on the result |
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15 | ; |
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16 | ; @param b {in}{required} see a |
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17 | ; |
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18 | ; @returns tableau |
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19 | ; |
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20 | ; @restrictions The empty set is denoted by an array with the first element equal to |
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21 | ; -1. |
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22 | ; |
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23 | ; @restrictions These functions will not be efficient on sparse sets with wide |
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24 | ; ranges, as they trade memory for efficiency. The HISTOGRAM function |
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25 | ; is used, which creates arrays of size equal to the range of the |
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26 | ; resulting set. |
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27 | ; |
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28 | ; @examples |
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29 | ; |
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30 | ; a = [2,4,6,8] |
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31 | ; b = [6,1,3,2] |
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32 | ; different(a,b) = [ 4, 8] ; Elements in A but not in B |
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33 | ; |
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34 | ; @history http://www.dfanning.com/tips/set_operations.html |
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35 | ; |
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36 | ; @version $Id$ |
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37 | ; |
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38 | ;- |
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39 | ;------------------------------------------------------------ |
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40 | ;------------------------------------------------------------ |
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41 | ;------------------------------------------------------------ |
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42 | FUNCTION different, a, b |
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43 | ; |
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44 | compile_opt idl2, strictarrsubs |
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45 | ; |
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46 | |
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47 | ; = a and (not b) = elements in A but not in B |
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48 | |
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49 | mina = Min(a, Max=maxa) |
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50 | minb = Min(b, Max=maxb) |
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51 | IF (minb GT maxa) OR (maxb LT mina) THEN RETURN, a ;No intersection... |
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52 | r = Where(Histogram(a, Min=mina, Max=maxa) $ |
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53 | *(1-Histogram(b, Min=mina, Max=maxa)), count) |
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54 | IF count eq 0 THEN RETURN, -1 ELSE RETURN, r + mina |
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55 | END |
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