Re: Re: Extracting terms from an equation

*To*: mathgroup at smc.vnet.net*Subject*: [mg69822] Re: [mg69786] Re: Extracting terms from an equation*From*: "Carl K. Woll" <carlw at wolfram.com>*Date*: Sat, 23 Sep 2006 23:45:30 -0400 (EDT)*References*: <eevubf$hqu$1@smc.vnet.net> <200609230844.EAA22454@smc.vnet.net>

dimmechan at yahoo.com wrote: > Can someone explain the difference in the following? > > Cases[a + b*x^2 + c*y^2 + d*x*y + e*x^3, _?( !FreeQ[#1, x] & )] > {b*x^2, e*x^3, d*x*y} > > Cases[a + b*x^2 + c*y^2 + d*x*y + e*x^3, _?(MemberQ[#1, x] & )] > {d*x*y} > MemberQ has a default level specification of {1}, while FreeQ has a default level specification of {0,Infinity}. If one uses the same level specifications, then !FreeQ and MemberQ are equivalent: expr = a + b*x^2 + c*y^2 + d*x*y + e*x^3; Give FreeQ the level spec (1): In[27]:= Cases[expr, _?(! FreeQ[#1, x, {1}] &)] == Cases[expr, _?(MemberQ[#1, x] &)] Out[27]= True Give MemberQ the level spec {0,Infinity}: In[28]:= Cases[expr, _?(! FreeQ[#1, x] &)] == Cases[expr, _?(MemberQ[#1, x, {0, Infinity}] &)] Out[28]= True Carl Woll Wolfram Research > Thanks > > Î?/Î? Coleman, Mark ÎÎ³Ï?Î±Ï?Îµ: >> Greetings, >> >> I'd like to find a general way to extract all of the terms from an >> equation that involve a given variable. For instance, consider the >> equation >> >> myEquation == Exp[a + b x^2 + c y^2 + d x y + e x^3]] >> >> I'd like to define a function such that >> >> myFunction[myEquation,x] returns the result {b x^2, d x y, e x^3} >> >> Thanks, >> >> -Mark

**References**:**Re: Extracting terms from an equation***From:*dimmechan@yahoo.com