Dervish

A simple command line tool that allows for evaluation and differentiation of mathematical functions. The tool can also interpret a text file.

Installation

To just get the application, download and run the jar file located at build/jar/Dervish.jar.

Alternatively, you can compile and run the code yourself. This project uses Apache Ant for building, which can be be downloaded here. Clone this repo and use ant clean-build to package the project into a jar.

The jar can then be run using java -jar build/jar/Dervish.jar.

Commands

use <variable(s)>               Declare what variables are being used.
forget <variable(s)>            Remove variables from `use` list.

set <variable> <expression>     Set a variable equal to a function.
clear <variable(s)>             Clear a variable`s value.
show <variable(s)>              Lists all variables and their values, if they
                                have one.

sub <expression> <variable(s)>  Substitutes specified variables and evaluates
                                the expression.
eval <expression>               Evaluates the expression without substitution,
                                which is the same as calling `sub` with no
                                variable arguments.
diff <expression> <variable>    Calculates the derivative of the expression
                                with respect to given variable.

help                            Lists descriptions of all commands.
exit                            Exit the program.

Guide

All arguments and commands are separated by spaces. This also means that you cannot put any spaces in a function.

To see all commands and a description of what they each do, simply type help. To exit the program, type exit.

If you are going to be using any variables, you need to tell the program about them before you use them. Use the use command followed by the names of the variables you want to use.

> use x y z

You can stop the program from recognizing variables with the forget command.

> forget x y z

To assign a value to a variable, use the set command.

> set x 4

Any function can be assigned as the value of a variable, as long as it doesn`t cause as cycle.

> set x y+2
> set y x-4

The above is not permitted because the each variable contains the other in its definition, causing a cycle.

To get rid of a variables value, use the clearcommand. Theclear` takes any number of variables to clear.

> clear x y

Alternatively, specify all to clear the value of every variable.

> clear all

The program automatically remembers the result of your last function operation and stores it as the value of the $ variable. The user cannot modify the $ variable manually.

> eval 1+2
3
> show $
3

You can show all variables that are currently defined and their values, if applicable, with the show command.

> use x y z
> set x 15
> show
$
y
z
x = 15

Simple evaluation of functions is done using the eval command.

> eval 3+8
11
> use x
> eval 5+x
5+x

Using the eval command does not substitute in values for variables. Instead, use the sub command. In addition to a function, the sub command takes any number of variables to have substituted in. Passing all or nothing substitutes in all variables.

> use x
> set x 4
> set y 3
> sub x+y x
4+y
> sub x+y all
7

Functions can be differentiated using the diff command. The diff command takes a function followed by the name of the variable to differentiate with respect to.

> use x
> diff x^2 x
x*2

The value of a variable can be set as the result of a evaluation, substitution, or differentiation.

> use x y
> set y diff x^3 x
> show y
x^2*3