Persona Equation 4D

This application is an Equation solver. (Linear/quadratic/cubic/quartic equation and inequality. Simultaneous equations until 4x4)
For both educational purpose and practical purpose like engineering, it equips the below functions that were not available in existing similar software.
* Calculation parameters expansion like slope,maximum,minimum,etc..
* Expansion of calculation direction to find equation coefficient from solution.
* Equipping input and calculation result with fractions, number with square root.

It equips User Interface suitable for Touchscreen. (Direct touch to displayed number works as number input or modification, or switching between result and input.)

(Spec)
・2x2/3x3/4x4 simultaneous equations consist from 4 coefficient sheets and answer sheet.
・Linear/quadratic/cubic/quartic equation consists from coefficient sheet, answer sheet and coordinate sheet.
・Number input and modification by direct touch action to the digit you want to change. In re-calculation of slight changes, entering full number is not necessary.
・Number input in keyboard sheet with keys that according to the number type to input.
・The direction of calculation is switchable by touch. Inverse calculation, changing result field to input, is easy.
・Calculation result is automatically done at the time necessary inputs reach.
・At the pressed moment of the key, the key function is shown display. (Not the released moment.)
・Lock of each number is possible.
・Internal calculation: 16-digit decimal or fraction or number with square root, independently developed (Not binary floating/double)
・Display number length is selected from 10/14-digit depending on screen size. (This digit becomes fewer when the number includes operator.)
・2 sheets can be parallelly shown and operated if screen size is larger.
・Copy / paste function of a each number and a sheet.
・1 memory.
・Graph display sheet of formula.
・Configurable rounding location.
・Selectable decimal point/separator character(5) and separator position(4), and number character(19).
・Automatic save of the calculation state at the application termination.
・Whole initializing. Or returning to the state at the time application started.
・Dark theme(Android10)