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simplex

 pivotvar
 return a variable with positive coefficient

 Calling Sequence pivotvar(f, List) pivotvar(f)

Parameters

 f - objective function expressed in terms of non-basic variables relative to some description List - list of the variables which occur in the problem

Description

 • The function pivotvar(f, List) returns either a variable which has a positive coefficient or FAIL.  The optional List (of variable names) is used to determine the order in which the variables should be examined.  The first success is used. If no List is provided, then pivotvar chooses its own order.
 • The command with(simplex,pivotvar) allows the use of the abbreviated form of this command.

Examples

 > $\mathrm{with}\left(\mathrm{simplex}\right):$
 > $\mathrm{pivotvar}\left(\mathrm{x1}+3\mathrm{x3}-\mathrm{x4}\right)$
 ${\mathrm{x1}}$ (1)
 > $\mathrm{pivotvar}\left(\mathrm{x1}+3\mathrm{x3}-\mathrm{x4},\left[\mathrm{x4},\mathrm{x3},\mathrm{x1}\right]\right)$
 ${\mathrm{x3}}$ (2)