version 0.84 release

Author: cdwensley

CHANGES.md

@@ -1,5 +1,8 @@
 # CHANGES log for the 'Utils' package
 
+## Version 0.84 for GAP 4.12.2 (11/09/23) 
+ * (11/09/23) changed manual and test for DirectSumDecompositionMatrices 
+
 ## Version 0.83 for GAP 4.12.2 (29/06/23) 
  * (29/06/23) added DirectSumDecompositionMatrices 
 

PackageInfo.g

@@ -7,8 +7,8 @@ SetPackageInfo( rec(
 
 PackageName := "utils", 
 Subtitle := "Utility functions in GAP",
-Version := "0.83",
-Date := "29/06/2023", # dd/mm/yyyy format
+Version := "0.84",
+Date := "11/09/2023", # dd/mm/yyyy format
 License := "GPL-2.0-or-later",
 
 Persons := [

doc/matrix.xml

@@ -33,7 +33,8 @@ So if <M>L</M> is the list of diagonal decompositions of a matrix <M>M</M>
 then each entry in <M>L</M> is a list of matrices, and the direct sum of 
 each of these lists is equal to the original <M>M</M>. 
 <P/> 
-In the examples, <M>M_6</M> is an obvious direct sum with <M>3</M> blocks. 
+In the following examples, <M>M_6</M> is an obvious direct sum 
+with <M>3</M> blocks. 
 <M>M_4</M> is an example with three decompositions, 
 while <M>M_8 = M_4 \oplus M_4</M> has <M>16</M> decompositions (not listed).
 <P/> 
@@ -87,6 +88,30 @@ gap> Length( L8 );
 16
 ]]>
 </Example>
+<P/>
+
+The current method does not, however, catch all possible decompositions. 
+In the following example the matrix <M>M_5</M> has its third row 
+and third column extirely zero, and the only decomposition found 
+has a <M>[0]</M> factor. 
+There are clearly two <M>2</M>-factor decompositions with a 
+<M>2</M>-by-<M>3</M> and a <M>3</M>-by-<M>2</M> factor, 
+but these are not found at present.
+<P/>
+<Example>
+<![CDATA[
+gap> M5 := [ [1,2,0,0,0], [3,4,0,0,0], [0,0,0,0,0],
+>            [0,0,0,6,7], [0,0,0,8,9] ];;
+gap> Display(M5);
+[ [  1,  2,  0,  0,  0 ],
+  [  3,  4,  0,  0,  0 ],
+  [  0,  0,  0,  0,  0 ],
+  [  0,  0,  0,  6,  7 ],
+  [  0,  0,  0,  8,  9 ] ]
+gap> L5 := DirectSumDecompositionMatrices( M5 ); 
+[ [ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 0 ] ], [ [ 6, 7 ], [ 8, 9 ] ] ] ]
+]]>
+</Example>
 
 </Section> 
 

tst/matrix.tst

@@ -1,9 +1,9 @@
-#@local M6, L6, M4, L4, M8, L8, L, A, M3, L3, M9, L9;
+#@local M6, L6, M4, L4, M8, L8, L, A, M3, L3, M5, L5;
 ##############################################################################
 ##
 #W  matrix.tst                   Utils Package                    
 ##
-#Y  Copyright (C) 2015-2022, The GAP Group 
+#Y  Copyright (C) 2015-2023, The GAP Group 
 ##  
 
 gap> ReadPackage( "utils", "tst/loadall.g" );;
@@ -64,22 +64,16 @@ gap> Display( M3 );
 gap> L3 := DirectSumDecompositionMatrices( M3 );                  
 [ [ [ [ 0, 0, 0, 7 ] ], [ [ 8 ] ], [ [ 9, 0 ] ] ] ]
 
-gap> M9 := [ [0,0,0,0,0,0,0,0,0], [0,0,0,0,0,0,0,0,0], [0,0,1,2,0,0,0,0,0], 
->            [0,0,3,4,0,0,0,0,0], [0,0,0,0,0,0,0,0,0], [0,0,0,0,0,5,6,7,0], 
->            [0,0,0,0,0,6,7,8,0], [0,0,0,0,0,7,8,9,0], [0,0,0,0,0,0,0,0,0] ];;
-gap> Display( M9 ); 
-[ [  0,  0,  0,  0,  0,  0,  0,  0,  0 ],
-  [  0,  0,  0,  0,  0,  0,  0,  0,  0 ],
-  [  0,  0,  1,  2,  0,  0,  0,  0,  0 ],
-  [  0,  0,  3,  4,  0,  0,  0,  0,  0 ],
-  [  0,  0,  0,  0,  0,  0,  0,  0,  0 ],
-  [  0,  0,  0,  0,  0,  5,  6,  7,  0 ],
-  [  0,  0,  0,  0,  0,  6,  7,  8,  0 ],
-  [  0,  0,  0,  0,  0,  7,  8,  9,  0 ],
-  [  0,  0,  0,  0,  0,  0,  0,  0,  0 ] ]
-gap> L9 := DirectSumDecompositionMatrices( M9 ); 
-[ [ [ [ 0 ] ], [ [ 0 ] ], [ [ 1, 2 ], [ 3, 4 ] ], [ [ 0 ] ], 
-      [ [ 5, 6, 7 ], [ 6, 7, 8 ], [ 7, 8, 9 ] ], [ [ 0 ] ] ] ]
+gap> M5 := [ [1,2,0,0,0], [3,4,0,0,0], [0,0,0,0,0],
+>            [0,0,0,6,7], [0,0,0,8,9] ];;
+gap> Display(M5);
+[ [  1,  2,  0,  0,  0 ],
+  [  3,  4,  0,  0,  0 ],
+  [  0,  0,  0,  0,  0 ],
+  [  0,  0,  0,  6,  7 ],
+  [  0,  0,  0,  8,  9 ] ]
+gap> L5 := DirectSumDecompositionMatrices( M5 ); 
+[ [ [ [ 1, 2 ], [ 3, 4 ] ], [ [ 0 ] ], [ [ 6, 7 ], [ 8, 9 ] ] ] ]
 
 #############################################################################
 ##