The procedure `Sort_Variable` sort a list of variable in
decreasing order according to the number of occurrences of the variable
in a given expression. This list may be used as the argument of the
`Maple` procedure `convert,horner` to convert an expression into a
form that is more convenient for interval evaluation. For example
consider the expression : by using the procedure we get the
sorted list [x,y] and

convert(x^2+x+y*x,horner,[x,y])leads to while

convert(x^2+x+y*x,horner,[y,x])leads to which is less efficient. The number of occurrences of a variable may be found in the global variable

Jean-Pierre Merlet 2012-12-20