1 | /* ========================================================================= */ |
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2 | /* === AMD_post_tree ======================================================= */ |
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3 | /* ========================================================================= */ |
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4 | |
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5 | /* ------------------------------------------------------------------------- */ |
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6 | /* AMD, Copyright (c) Timothy A. Davis, */ |
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7 | /* Patrick R. Amestoy, and Iain S. Duff. See ../README.txt for License. */ |
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8 | /* email: davis at cise.ufl.edu CISE Department, Univ. of Florida. */ |
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9 | /* web: http://www.cise.ufl.edu/research/sparse/amd */ |
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10 | /* ------------------------------------------------------------------------- */ |
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11 | |
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12 | /* Post-ordering of a supernodal elimination tree. */ |
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13 | |
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14 | #include "amd_internal.h" |
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15 | |
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16 | GLOBAL Int AMD_post_tree |
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17 | ( |
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18 | Int root, /* root of the tree */ |
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19 | Int k, /* start numbering at k */ |
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20 | Int Child [ ], /* input argument of size nn, undefined on |
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21 | * output. Child [i] is the head of a link |
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22 | * list of all nodes that are children of node |
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23 | * i in the tree. */ |
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24 | const Int Sibling [ ], /* input argument of size nn, not modified. |
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25 | * If f is a node in the link list of the |
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26 | * children of node i, then Sibling [f] is the |
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27 | * next child of node i. |
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28 | */ |
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29 | Int Order [ ], /* output order, of size nn. Order [i] = k |
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30 | * if node i is the kth node of the reordered |
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31 | * tree. */ |
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32 | Int Stack [ ] /* workspace of size nn */ |
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33 | #ifndef NDEBUG |
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34 | , Int nn /* nodes are in the range 0..nn-1. */ |
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35 | #endif |
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36 | ) |
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37 | { |
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38 | Int f, head, h, i ; |
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39 | |
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40 | #if 0 |
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41 | /* --------------------------------------------------------------------- */ |
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42 | /* recursive version (Stack [ ] is not used): */ |
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43 | /* --------------------------------------------------------------------- */ |
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44 | |
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45 | /* this is simple, but can caouse stack overflow if nn is large */ |
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46 | i = root ; |
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47 | for (f = Child [i] ; f != EMPTY ; f = Sibling [f]) |
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48 | { |
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49 | k = AMD_post_tree (f, k, Child, Sibling, Order, Stack, nn) ; |
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50 | } |
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51 | Order [i] = k++ ; |
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52 | return (k) ; |
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53 | #endif |
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54 | |
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55 | /* --------------------------------------------------------------------- */ |
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56 | /* non-recursive version, using an explicit stack */ |
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57 | /* --------------------------------------------------------------------- */ |
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58 | |
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59 | /* push root on the stack */ |
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60 | head = 0 ; |
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61 | Stack [0] = root ; |
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62 | |
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63 | while (head >= 0) |
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64 | { |
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65 | /* get head of stack */ |
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66 | ASSERT (head < nn) ; |
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67 | i = Stack [head] ; |
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68 | AMD_DEBUG1 (("head of stack "ID" \n", i)) ; |
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69 | ASSERT (i >= 0 && i < nn) ; |
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70 | |
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71 | if (Child [i] != EMPTY) |
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72 | { |
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73 | /* the children of i are not yet ordered */ |
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74 | /* push each child onto the stack in reverse order */ |
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75 | /* so that small ones at the head of the list get popped first */ |
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76 | /* and the biggest one at the end of the list gets popped last */ |
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77 | for (f = Child [i] ; f != EMPTY ; f = Sibling [f]) |
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78 | { |
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79 | head++ ; |
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80 | ASSERT (head < nn) ; |
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81 | ASSERT (f >= 0 && f < nn) ; |
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82 | } |
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83 | h = head ; |
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84 | ASSERT (head < nn) ; |
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85 | for (f = Child [i] ; f != EMPTY ; f = Sibling [f]) |
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86 | { |
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87 | ASSERT (h > 0) ; |
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88 | Stack [h--] = f ; |
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89 | AMD_DEBUG1 (("push "ID" on stack\n", f)) ; |
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90 | ASSERT (f >= 0 && f < nn) ; |
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91 | } |
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92 | ASSERT (Stack [h] == i) ; |
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93 | |
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94 | /* delete child list so that i gets ordered next time we see it */ |
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95 | Child [i] = EMPTY ; |
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96 | } |
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97 | else |
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98 | { |
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99 | /* the children of i (if there were any) are already ordered */ |
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100 | /* remove i from the stack and order it. Front i is kth front */ |
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101 | head-- ; |
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102 | AMD_DEBUG1 (("pop "ID" order "ID"\n", i, k)) ; |
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103 | Order [i] = k++ ; |
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104 | ASSERT (k <= nn) ; |
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105 | } |
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106 | |
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107 | #ifndef NDEBUG |
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108 | AMD_DEBUG1 (("\nStack:")) ; |
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109 | for (h = head ; h >= 0 ; h--) |
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110 | { |
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111 | Int j = Stack [h] ; |
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112 | AMD_DEBUG1 ((" "ID, j)) ; |
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113 | ASSERT (j >= 0 && j < nn) ; |
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114 | } |
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115 | AMD_DEBUG1 (("\n\n")) ; |
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116 | ASSERT (head < nn) ; |
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117 | #endif |
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118 | |
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119 | } |
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120 | return (k) ; |
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121 | } |
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