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Products of permutations

In order to form the product of permutations tex2html_wrap_inline1001 we mean apply tex2html_wrap_inline933 first and then apply tex2html_wrap_inline1005 . In terms of the cycle representation this means that products are carried out reading from left to right. This assumes that you are now writing functions on the right! To carry out a product we construct cycles as described above but with one difference. Select an element tex2html_wrap_inline937 . The next element in the cycle is tex2html_wrap_inline1009 followed by tex2html_wrap_inline1011 etc. Repeat this procedure until every element of A appears in some cycle, again single cycles are suppressed.

To illustrate this, if tex2html_wrap_inline1015 and tex2html_wrap_inline1017 then find tex2html_wrap_inline1001 and tex2html_wrap_inline1021 .

displaymath1023

displaymath1025

Note that the cycle in tex2html_wrap_inline1005 was written as tex2html_wrap_inline1029 but could have been written as tex2html_wrap_inline1031 .

Another way to carry out this multiplication process (although no different from what has already been said) is as follows. Write down your starting element. Read the cycles from left to right. If the starting element is in a cycle read its successor (you may have to wrap around to the beginning of the cycle). This is you new number. Now go to the next cycle in which this new number appears. Read its successor and this becomes the new number. Repeat until you reach the end of the cycles (you have reached the rightmost end). This is now written as the successor of the starting element. Now this number becomes the new starting element. Repeat the above to find its successor. When you obtain a successor which is the original starting element, close off your cycle. Open up a new cycle and start all over again until all numbers have appeared in exactly one cycle. Now erase cycles of length one.



Peter Williams
Sun Mar 30 14:48:35 PST 1997