## Instructions

DEW1 draws the solution of differential equation of first order
with initial values t_{0} and y_{0}. The program also draws the direction field.

### Drawing (*Initial values*)

Solution is drawn with initial values t_{0} and y_{0}.
Values can be entered in the **t=** and **y=** text fields, then clicking the **Draw**-button will draw the corresponding solution. Or the initial conditions can be clicked on with the mouse.

### Equation

A differential equation may be selected from the pre-defined examples or may by defined by user. For example, the equation

*y'* - 3**y* + 2**t* = 0

is first solved for *y'*:

*y'* = 3**y* - 2**t*,

then the right side of equation is given to the program:

3**y* - 2**t*.

Finally click the **Read equation**-button.

### Changing the scale (*Scale*)

The scale can be adjusted by chancing the values of **tmin**, **tmax**, **ymin** and **ymax** and clicking the **Change scale** -button.

### Numerical method (*General*)

The solution may be plotted by using one of the following algoritms: adaptive Runge-Kutta, Euler, improved Euler, Runge-Kutta or Adams-Bashforth.

For non-adaptive methods the stepsize may be adjusted via the **Stepsize** -textfield.

### Clearing (*General*)

**Clear** -button clears everything that has been drawn.

### Equation parser

The equation parser recognizes the following mathematical operations, elementary functions and variables:

-Basic operations: **+**, **-**, *****, **/**, and power **^**.

-Trigonometrical functions: **sin()**, **cos()**, **tan()**, **asin()**, **acos()**, **atan()**.

-Elementary functions: **exp()**, **abs()**, **sqrt()** and **log()**.

-Other functions: **abs()**, **sign()**.

-Brackets: **()**.

-Variables: **t**, **y**.

There must always be an operator between two operands. For example, **2t+3y** must be given to the program in the form of **2*t+3*y**.