Skip to main content

How to change the variables Qi's to Ri's in one or two steps


I was wondering if there is a command in Mathematica to change all the following Qi's to Ri's? For example, change Q1 to R1, Q2 to R2, etc.


 Q1 a1 + Q2 a2 + Q3 a3 + Q4 a4 + Q5 a5 + Q6 a6 + Q7 a7 + Q8 a8 + 
 Q9 a9 + Q10 a10 + Q11 a11 + Q12 a12 + Q13 a13 + Q14 a14 + Q15 a15 + 
 Q16 a16 + Q17 a17 + Q18 a18 + Q19 a19 + Q20 a20 + Q21 a21 + Q22 a22 +
 Q23 a23 + Q24 a24 + Q25 a25 + Q26 a26 + Q27 a27 + Q28 a28 + 
 Q29 a29 + Q30 a30 + Q31 a31 + Q32 a32 + Q33 a33 + Q34 a34 + Q35 a35 +
 Q36 a36 + Q37 a37 + Q38 a38 + Q39 a39 + Q40 a40 + Q41 a41 + 

 Q42 a42 + Q43 a43 + Q44 a44

I could go through and change the Qi's by hand, but I think there should be a more efficient way to do this.


Thank you.



Answer



I believe I would use:


expr = Q1 a1 + Q2 a2 + Q3 a3 + Q4 a4 + Q5 a5 + Q6 a6 + Q7 a7 + Q8 a8 +
    Q9 a9 + Q10 a10 + Q11 a11 + Q12 a12 + Q13 a13 + Q14 a14 + 
   Q15 a15 + Q16 a16 + Q17 a17 + Q18 a18 + Q19 a19 + Q20 a20 + 
   Q21 a21 + Q22 a22 + Q23 a23 + Q24 a24 + Q25 a25 + Q26 a26 + 

   Q27 a27 + Q28 a28 + Q29 a29 + Q30 a30 + Q31 a31 + Q32 a32 + 
   Q33 a33 + Q34 a34 + Q35 a35 + Q36 a36 + Q37 a37 + Q38 a38 + 
   Q39 a39 + Q40 a40 + Q41 a41 + Q42 a42 + Q43 a43 + Q44 a44;

expr /. S_Symbol :> Symbol @ StringReplace[SymbolName@S, "Q" -> "R"]

Or more restrictively:


rule = "Q" ~~ x : DigitCharacter .. :> "R" <> x;

expr /. S_Symbol :> Symbol @ StringReplace[SymbolName@S, rule]


I feel that operating only on Symbols is cleaner and safer than converting the entire expression to and from a String.



It is not clear to me if you need this, but if you want to do the replacement after (while) Qi's are assigned values you can do it like this:


{Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, Q11, Q12} = Range@12;

expr = Hold[Q1 a1 + Q2 a2 + Q3 a3 + Q4 a4 + Q5 a5 + Q6 a6 +
         Q7 a7 + Q8 a8 + Q9 a9 + Q10 a10 + Q11 a11 + Q12 a12];

expr /. S_Symbol :> 

  RuleCondition @ Symbol @ StringReplace[SymbolName@Unevaluated@S, "Q" -> "R"]


Hold[R1 a1 + R2 a2 + R3 a3 + R4 a4 + R5 a5 + R6 a6 +
    R7 a7 + R8 a8 + R9 a9 + R10 a10 + R11 a11 + R12 a12]

Comments

Post a Comment

Popular posts from this blog

functions - Get leading series expansion term?

Given a function f[x] , I would like to have a function leadingSeries that returns just the leading term in the series around x=0 . For example: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x)] x and leadingSeries[(1/x + 2 + (1 - 1/x^3)/4)/(4 + x)] -(1/(16 x^3)) Is there such a function in Mathematica? Or maybe one can implement it efficiently? EDIT I finally went with the following implementation, based on Carl Woll 's answer: lds[ex_,x_]:=( (ex/.x->(x+O[x]^2))/.SeriesData[U_,Z_,L_List,Mi_,Ma_,De_]:>SeriesData[U,Z,{L[[1]]},Mi,Mi+1,De]//Quiet//Normal) The advantage is, that this one also properly works with functions whose leading term is a constant: lds[Exp[x],x] 1 Answer Update 1 Updated to eliminate SeriesData and to not return additional terms Perhaps you could use: leadingSeries[expr_, x_] := Normal[expr /. x->(x+O[x]^2) /. a_List :> Take[a, 1]] Then for your examples: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x), x] leadingSeries[Exp[x], x] leadingSeries[(1/x + 2 + (1 - 1/x...
Post a Comment
Read more

mathematical optimization - Minimizing using indices, error: Part::pkspec1: The expression cannot be used as a part specification

I want to use Minimize where the variables to minimize are indices pointing into an array. Here a MWE that hopefully shows what my problem is. vars = u@# & /@ Range[3]; cons = Flatten@ { Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; Minimize[{Total@((vec1[[#]] - vec2[[u[#]]])^2 & /@ Range[1, 3]), cons}, vars, Integers] The error I get: Part::pkspec1: The expression u[1] cannot be used as a part specification. >> Answer Ok, it seems that one can get around Mathematica trying to evaluate vec2[[u[1]]] too early by using the function Indexed[vec2,u[1]] . The working MWE would then look like the following: vars = u@# & /@ Range[3]; cons = Flatten@{ Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; NMinimize[ {Total@((vec1[[#]] - Indexed[vec2, u[#]])^2 & /@ R...
Post a Comment
Read more

How to remap graph properties?

Graph objects support both custom properties, which do not have special meanings, and standard properties, which may be used by some functions. When importing from formats such as GraphML, we usually get a result with custom properties. What is the simplest way to remap one property to another, e.g. to remap a custom property to a standard one so it can be used with various functions? Example: Let's get Zachary's karate club network with edge weights and vertex names from here: http://nexus.igraph.org/api/dataset_info?id=1&format=html g = Import[ "http://nexus.igraph.org/api/dataset?id=1&format=GraphML", {"ZIP", "karate.GraphML"}] I can remap "name" to VertexLabels and "weights" to EdgeWeight like this: sp[prop_][g_] := SetProperty[g, prop] g2 = g // sp[EdgeWeight -> (PropertyValue[{g, #}, "weight"] & /@ EdgeList[g])] // sp[VertexLabels -> (# -> PropertyValue[{g, #}, "name"]...
Post a Comment
Read more