I was following this thread and copied the code in my project. Playing around with it turns out that it seems not to be very precise.

Recall the formula: y = ax^2 + bx +c

Since the first given point I have is at x1 = 0, we already have c=y1 . We just need to find a and b. Using:

y2 = ax2^2 + bx2 +c y3 = ax3^2 + bx3 +c

Solving the equations for b yields:

b = y/x - ax - cx

Now setting both equations equal to each other so b falls out

y2/x2 - ax2 - cx2 = y3/x3 - ax3 - cx3

Now solving for a gives me:

a = ( x3*(y2 - c) + x2*(y3 - c) ) / ( x2*x3*(x2 - x3) )

(is that correct?!)

And then using again b = y2/x2 - ax2 - cx2 to find b. However so far I haven't found the correct a and b coeffs. What am I doing wrong?