Table of Variables

Question

I use a list of variables {x1, x2, x3} to Solve a particular set of equations.

I am now trying to generalise this depending on the number of equations.

I need something along the lines of Table[{"x" i}, {i,1,Length[equations]}] which prints {x1, x2, x3, x4,...} etc.

However, "x" i obviously does not work. Nor does x[[i]] as {x[[1]], x[[2]], x[[3]]} won't work in Solve.

Any quick thoughts?

Thank you.

Answer 1

Use Symbol to convert a string into a symbol...

Table[Symbol["$x" <> ToString@i], {i, 5}]

{$x1, $x2, $x3, $x4, $x5}

One word of caution. I tend to keep programmatically generated variables prepended with a $ to avoid any collisions with any other variables I might've defined. Just from experience.

Answer 2

You almost have found a simple solution: try x[i] instead of x[[i]]

Solve[{x[1] + x[2] == 2, x[1] - x[2] == 1}, {x[1], x[2]}]

{{x[1] -> 3/2, x[2] -> 1/2}}

List of this variables:

Array[x,2]

{x[1], x[2]}

Answer 3

Or you could make a function to add a range of numbers to a predefined string("x")

f2 := Function[{i}, ToExpression["x" <> ToString[#]] & /@ Range[i]]

f2[5]

{x1,x2,x3,x4,x5}

Or a function to add a range of numbers to any string

f3 := Function[{i, s}, ToExpression[s <> ToString[#]] & /@ Range[i]]

f3[5, "y"]

{y1,y2,y3,y4,y5}