Concepts

Four ideas explain almost everything Quantus does with an input.

Modes decide how letters are read

The same input means different things in different modes. 2kg is two kilograms in Physics and the product $2 \cdot g \cdot k$ in Algebra.

Mode	Letters are	Units and constants	$i$
Physics (default)	units or constants where they match one, otherwise variables	known	a variable
Algebra	variables	unknown	a variable
Imaginary	variables	unknown	the imaginary unit
Analysis	variables, as in Algebra	unknown	a variable

Switch the mode in the top bar or under Settings → Mode. An example under the empty input shows what fits the current mode.

Variables carry an index

In Physics mode most short letter runs are units: m, s, g, h, t, V, A. So a quantity you want to keep needs an index, which makes it unmistakably a variable:

Input	Meaning
m_1 = 2kg	Definition: $m_1$ is stored for the session
F = m_1 \cdot g_1	Named line: the result is labelled $F$, nothing is stored
x = 3	A named line too; plain letters are never stored
2x + 3 = 11	An equation: $x$ is the unknown, Quantus solves for it

Letters without an index still work as unknowns of an equation and as the bound letter of $\sum$, $\int$, $\lim$ and $\frac{d}{dx}$.

Three settings under Settings → Input change how letters are read:

Setting	Default	Effect
a and y as variables	on	otherwise a and y are the unit year
Letter runs as a product	on	2ab is read as $2 \cdot a \cdot b$
t, u and in as units	off	tonne, atomic mass unit and inch instead of variables

A session holds your variables

Everything you define lives in the current session and shows up in the Variables panel. The History panel (Ctrl+H) keeps the calculations. Delete a variable from the panel to forget it. See Variables and history.

Numbers are exact

Quantus calculates with exact fractions and arbitrary-precision decimals, not with floating point. Decimals only appear when the result is written, with as many significant digits as Settings → Precision says (50 by default).

Roots and $\pi$ are written as decimals unless Exact as a root is on:

Input	Default	With Exact as a root
\sqrt{12}	$3{,}4641016151\ldots$	$2\sqrt{3}$

Results found numerically, such as most integrals, are marked by their digits: an integral shows at most 30. See Known limits.

The working is part of the result

Each result comes with its steps, labelled SYMBOLIC (the formula as entered), SUBSTITUTED (the variables put in), STEP (one rule each) and RESULT. How many steps you see is the Step detail setting, from None to Maximal; see Working and output.