# How can I change a lot of parameters to Real? [closed]

Because of some formulas with Conjugate in a notebook, I have to tell mathematica to change a lot of parameters to Real! I know that I can use Refine with Element or Assumptions:

Refine[k + x + g, Element[x | k | g, Reals]]

or

Refine[%, Assumptions -> {x, k, g} \[Element] Reals]

, But it's useful for a few parameters not a lot!

For Example I'd like to define:

Ki,j & i{1 to 20} , j{1 to 20}

in Reals. Is there any function to define it without telling mathematica one by one?

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• Start by not using parameters with subscripts. They look pretty, but they are a pain to deal with. Rename the variables: e.g. use bi instead of Subscript[b,i]. Another tip: don't use uppercase single letter variable names: they can conflict with built-in symbols. For instance, K is already an existing symbol (try and execute ?K). – MarcoB May 11 '15 at 15:01
• You can specify a domain for some functions. There are Cases, Variables and other functions that might be useful in extracting the parameters from your code. -- As written currently, this question is a bit too broad. Can you provide a minimal working example, that would be typical of the problem that concerns you? – Michael E2 May 11 '15 at 16:29
• For Example I'd like to define Ki,j & i{1 to 20} & j{1 to 20} in Reals. Is there any function to define it without telling mathematica one by one? – Maryam.D May 16 '15 at 7:07
• Please add that information to the question and supply some examples to avoid unnecessary effort. General advice: avoid subscripts. They are a big source of confusion. – Yves Klett May 16 '15 at 7:35

I'm not sure what you mean by Ki,j but perhaps this

vars = ToExpression@
Flatten@Table["K" <> ToString[i] <> "\$" <> ToString[j], {i, 20}, {j, 20}];

or this

vars = Flatten@Table[k[i, j], {i, 20}, {j, 20}];

Then one can use it thus:

Assuming[vars ∈ Reals,
Refine[
Apply[
Times,
Sqrt[vars ^ RandomInteger[4, Length[vars]]]
]] /. p_Power :> Simplify[p]
]
(* large expression with Sqrt[x^2] simplified to Abs[x] etc. *)