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Re: Applying a set of rules to a List
*To*: mathgroup at yoda.physics.unc.edu
*Subject*: Re: Applying a set of rules to a List
*From*: John Lee <lee at math.washington.edu>
*Date*: Wed, 27 Jan 93 10:28:42 -0800
Tony Varghese <avarg at s1.arc.umn.edu> writes:
> I would like to apply a set of rules to all the elements of a list and
> I've tried a number of things with no success.
> What I have is a set of equations in which certain variables are to be
> held at fixed values. The equations are stored as a list, say, oldEqns.
> The substitution rules are stored in a variable called fpRules.
> I need to get a new set of equations obtained by ReplaceAll'ing the
> old eqns with the fpRules. Here is one attempt:
> applyRules[item_] := ReplaceAll[item, fpRules]
> newEqns = Map[ applyRules, oldEqns ]
> Unfortunately this did not work; I don't see any difference between
> oldEqns and newEqns even though I KNOW there are places where the rules
> can be applied.
> Anyone see the problem?
Your setup should work as it stands. Here's a simple example:
In[89]:= oldEqns = {a,b,c,d}
Out[89]= {a, b, c, d}
In[90]:= fpRules = {a->A, c->C}
Out[90]= {a -> A, c -> C}
In[91]:= applyRules[item_] := ReplaceAll[item, fpRules]
In[92]:= newEqns = Map[ applyRules, oldEqns ]
Out[92]= {A, b, C, d}
So my guess is that your rules aren't really doing what you want them to.
Perhaps the left-hand sides don't really match the internal form (FullForm)
of your equations.
Jack Lee
Dept. of Mathematics
University of Washington
Seattle, WA
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