Tech Note C

Underscores, and subscripts in your answers

An underscore does two jobs. In an answer's name it is optional, so ir1 and i_r1 mean the same current. In a symbolic value it is not: it puts what follows into a subscript, and makes an answer read the way a textbook prints it.

Last updated 2026-09-11

The underscore does two different jobs in Symbulator, and it is worth knowing which is which. In the name of an answer it is optional and changes nothing. In the value you give an element, it changes how the answer is typeset.

In an answer's name, it is optional

You may write the name of any of Symbulator's answers in two ways: with or without an underscore. ir1 and i_r1 are the same current, v2 and v_2 the same voltage; capitals make no difference either.

Version 9 added the longer spelling so that a name written out by a machine reads back without ambiguity; the shorter one is what the calculators used, and it is what this tutorial uses throughout. Neither is more correct than the other, and you can mix them freely — wherever you type an answer's name, in Evaluate, in Solve, in a condition, or (in the case of dependent sources) as part of an element's value, Symbulator recognises both formats.

In a symbolic value, it makes a subscript

Textbooks set their symbols with subscripts: v_cc, r_b, i_rb. Symbolic answers can be made to read the same way, and the trick is very simple: put an underscore in your symbolic variable names. The text after the underscore is set as a subscript.

That is all there is to it. v_cc prints as v_cc, r_e1 as r_e1. It costs nothing, it changes no answer, and it makes a symbolic result that much easier to compare with the page you are working from.

One difference from the section above, and it is the only trap here. In an answer's name the underscore is optional; in a symbolic variable it is part of the name. Rename vcc to v_cc everywhere and nothing changes but the typesetting — but write v_cc in the circuit and vcc in a condition and you have named two variables, not one, and Symbulator will treat them as two. Pick a spelling for each symbol and stay with it.

TR5's Example 4.5 (Symbolic)

Open in app ↗Open in split view

The same circuit twice: once with plain names, once with subscripted ones, so the difference is only in how the answer reads.

Given this circuit description, with plain names:

Circuit Description

e1,1,0,vcc
rb,1,b,rb
e2,e,b,vγ
re1,e,0,re1
rc,1,c,rc
j,c,e,β*irb

the current through rb comes back as

current through rb

\[i_{rb} = \dfrac{vcc + v\gamma}{r_{e1}\,\beta + r_{e1} + rb}\]

One subscript arrives without being asked for: re1 prints as r_e1, because trailing digits are set as a subscript anyway. The underscore is what gets you the rest.

Run the same circuit with underscores in the symbolic values instead:

Circuit Description

e1,1,0,v_cc
rb,1,b,r_b
e2,e,b,v_γ
re1,e,0,r_e1
rc,1,c,r_c
j,c,e,β*irb

and the answer is typeset the way the book prints it:

current through rb

\[i_{rb} = \dfrac{v_{cc} + v_{\gamma}}{r_{b} + r_{e1}\,\beta + r_{e1}}\]

The two answers are the same expression. Only their appearance differs.