GRPN is a graphical reverse polish notation (RPN) calculator. GRPN works with real numbers, complex numbers, matrices, and complex matrices. Numbers can be displayed in 4 different radix modes, and complex numbers can be displayed in either Cartesian or polar form. GRPN uses a stack and reverse polish notation to evaluate expressions. The stack in GRPN is infinite and limited only by available memory. Expressions are evaluated in reverse polish notation. Unlike conventional (prefix) notation, RPN requires that all arguments to a command are entered prior to execution of the command. For example to add 6.7 to 3.2 you would push both numbers onto the stack, then press the add (+) button: 3.2<enter> 6.7<enter> + The result is left on the stack. Note that GRPN uses a shorthand for all commands that causes an automatic <enter> before executing a command. The previous example could then be done as: 3.2<enter> 6.7+ Input is accepted from both the keyboard and the mouse. When entering a command from the keyboard, the command may be abbreviated to the shortest set of letters which uniquely identifies the command. Mouse input simply requires pressing the button with the desired command. Available commands: + Add. - Subtract. * Multiply. / Divide. ^ Power. <enter> Push a number onto the top of the stack. <space> Push a number onto the top of the stack. dup Copy the number on the top of the stack. neg Change sign. drop Delete the number on the top of the stack. swap Swap 2 numbers on the top of the stack. pi The constant PI. sin Trigonometric function Sin. cos Trigonometric function Cos tan Trigonometric function Tan. inv Inverse. asin Trigonometric function Arc-sin acos Trigonometric function Arc-cos. atan Trigonometric function Arc-tan. sqrt Square root. nroot N-th root. log Log base 10 ln Natural log (log base e). sqr Square.