Selecting subscripted variables from an expression
- To: mathgroup at smc.vnet.net
- Subject: [mg109087] Selecting subscripted variables from an expression
- From: "Dominic" <miliotodc at rtconline.com>
- Date: Mon, 12 Apr 2010 22:59:30 -0400 (EDT)
Hi guys. I have an expression containing terms with subscripted "a" and "b" variables. Can someone help me devise an algorithm to select from this sum, all the terms that have a particular subscripted variable as the first term, such as all the terms that begin with an a_1 in them. For example, if I have the expression: myNumerator=2a_1a_2b_2 + a_2 + a_1b_2b_3 + a_3b_2_b_3 then the routine would pick out the 2a_1a_2b_2 term and the a_1b_2b_3 terms. The expression below is a particular example. So I suppose the routine might look like some version of: Select[myNumerator, (all terms that begin with a_1 for example)] myNumerator = Subscript[a, 1]*Subscript[b, 0]^5 - Subscript[a, 2]*Subscript[b, 0]^4*Subscript[b, 1] + Subscript[a, 3]*Subscript[b, 0]^3*Subscript[b, 1]^2 - Subscript[a, 4]*Subscript[b, 0]^2*Subscript[b, 1]^3 + Subscript[a, 5]*Subscript[b, 0]*Subscript[b, 1]^4 - Subscript[a, 6]*Subscript[b, 1]^5 - Subscript[a, 3]*Subscript[b, 0]^4* Subscript[b, 2] + 2*Subscript[a, 4]*Subscript[b, 0]^3*Subscript[b, 1]* Subscript[b, 2] - 3*Subscript[a, 5]*Subscript[b, 0]^2*Subscript[b, 1]^2* Subscript[b, 2] + 4*Subscript[a, 6]*Subscript[b, 0]*Subscript[b, 1]^3* Subscript[b, 2] + Subscript[a, 5]*Subscript[b, 0]^3*Subscript[b, 2]^2 - 3*Subscript[a, 6]*Subscript[b, 0]^2*Subscript[b, 1]*Subscript[b, 2]^2 - Subscript[a, 4]*Subscript[b, 0]^4*Subscript[b, 3] + 2*Subscript[a, 5]*Subscript[b, 0]^3*Subscript[b, 1]*Subscript[b, 3] - 3*Subscript[a, 6]*Subscript[b, 0]^2*Subscript[b, 1]^2*Subscript[b, 3] + 2*Subscript[a, 6]*Subscript[b, 0]^3*Subscript[b, 2]*Subscript[b, 3] - Subscript[a, 5]*Subscript[b, 0]^4*Subscript[b, 4] + 2*Subscript[a, 6]*Subscript[b, 0]^3*Subscript[b, 1]*Subscript[b, 4] - Subscript[a, 6]*Subscript[b, 0]^4*Subscript[b, 5]; Thanks guys, Dominic