Checking variables in an expression
- To: mathgroup at smc.vnet.net
- Subject: [mg112461] Checking variables in an expression
- From: Ignacio Plazeta <Ignacio.Plazeta at speednet.es>
- Date: Thu, 16 Sep 2010 06:00:15 -0400 (EDT)
Dear Friends
I need a function myCheck[] returning the list of variable in expr not
listed in vars.
Es.
--------------------------------------------------
expr = a + Cos[b] + c[t] - c'[t] + d ^ p - c;
vars = {a , b , c, c[t] , c'[t] , d , p};
myCheck[ expr , vars ]
{}
because only variables in vars are in expr
--------------------------------------------------
expr = a + Cos[b] + c[t] - c'[t] + d ^ p - c + w + w[t];
vars = {a , b , c, c[t] , c'[t] , d , p};
myCheck[ expr , vars ]
{w , w[t]}
because w and w[t] are in expr but not in vars
--------------------------------------------------
I have tryed the childish:
Remove[a, b, c, d, e, f, g, expr, vars]
expr = a + b + c + d + e + f + g;
vars = {a, b, c, d, e};
myRules = (Rule[#, ""]) & /@ vars
res = expr //. myRules;
but it dosn't work really fine because I don't know how to remove
integers, Rational[""/""] etc. from res
Any hints is greatly appreciated.
Warmest regards.
Ignacio