Quadratic eq & graph (Beta)

Hi everyone!

I've been working on a multi function program that can resolve and graph mathematic functions (like senx, cosx, ax²+bx+c, mx+b, 1/x, Math.Pow(e, x), etc). Last week I made the quadratic function algorithm.

When I get the program finished I'll upload here with download link, it's called Blitzmath.

So, here's the code:

Equation to get x1 and x2:

x1 = (-b + (Math.Sqrt((Math.Pow(b, 2)) - (4 * a * c)))) / (2 * a);
x2 = (-b - (Math.Sqrt((Math.Pow(b, 2)) - (4 * a * c)))) / (2 * a);

Note: You must declare a, b, c, x1, x2 as double.

After that, you should want to get vertices, here's the equation:

xv = (x1 + x2) / 2;
yv = (a*(Math.Pow(xv, 2)))+(b*xv)+c;

We need those vertices to set up the origin with R² plane

Well, now we're goin' to graph this function.

First of all you need to put a Panel and a Timer in your form, just like this:

Now we should set up those controls like this:

Double click on the Timer in order to modify its code

private void timer1_Tick(object sender, EventArgs e)
        {
            System.Drawing.Pen linep;
            linep = new System.Drawing.Pen(System.Drawing.Color.Black);
            System.Drawing.Graphics g = panel1.CreateGraphics();
            g.DrawLine(linep, 0, panel1.Height / 2, panel1.Width, panel1.Height / 2);
            g.DrawLine(linep, panel1.Width / 2, 0, panel1.Width / 2, panel1.Height);
            timer1.Enabled = false;
        }

And then go to public form1() and paste this:

public Form1()
        {
            
            InitializeComponent();
            timer1.Enabled = true;
        }

This code will draw the panel as x,y coordinates plane

Well, let's draw that parabola:
Note: The code has some troubles drawing negative vertices, I'll try to solve that as soon as I can.

System.Drawing.Graphics g = panel1.CreateGraphics();
int origy, origx;
Bitmap pen = new Bitmap(1, 1);
int vx = Convert.ToInt32(xv);
int vy = Convert.ToInt32(yv);
origx = (panel1.Width / 2) ;
origy = (panel1.Height / 2) ;
pen.SetPixel(0, 0, Color.Blue);
for (double i = 0; i <= 1000; i += 0.01)
            {
                x = i+xv;
                if (yv < 0)
                {
                    origy = (panel1.Height / 2) + vy;
                }
                y = (a * (Math.Pow((double)x, 2D)) + (b * x) + c) + yv;          
                g.DrawImageUnscaled(pen, origx + (int)x, origy - (int)y);
                g.DrawImageUnscaled(pen, origx - (int)x, origy - (int)y);
                if (y >= origy)
                {
                    break;
                }
            }

That should work in order to draw an aproximated graph.
If you want a values table you should declare two lists linked to separate listBoxes

List<double> table = new List<double>();
List<double> table2 = new List<double>();

After that you must evaluate the function on x values from 0 to <10, we'll do this with a FOR:

for (double j = 0; j < 10; j++)
            {
                double fx = (a * (j * j)) + (b * j) + c;
                table.Add(j);
                table2.Add(fx);
            }

I recommend 'ya to put a new button for showing the lists, in the button_click event paste this:

listBox1.DataSource = table;
listBox2.DataSource = table2;

I made this program in 45 minutes, so it has some bugs and the code is very untidy, if you have any question about the code or any recomendation just leave a comment here!

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C#, Programming

domingo, 18 de septiembre de 2016

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