Download or view simplegraph3.frink in plain text format
// This is a simple but rather interesting program that graphs equations.
// You enter equations in terms of x and y, something like one of the
// following:
//
// y = sin[x]
//
// x^2 + y^2 = 81
//
// y cos[x] = x sin[y]
//
// This uses a recursive method to subdivide and test rectangles.
use ArbitraryPrecision.frink
lasteq = ""
while func = input["Enter equation: ", lasteq]
{
lasteq = func
func =~ %s/>=/ PGE /g // Replace >= with possibly greater than or equals
func =~ %s/<=/ PLE /g // Replace <= with possibly less than or equals
func =~ %s/!=/ PNE /g // Replace != with possibly not equals
func =~ %s/>/ PGT /g // Replace > with possibly greater than
func =~ %s/</ PLT /g // Replace < with possibly less than
func =~ %s/=/ PEQ /g // Replace = with possibly equals
eq = parseToExpression[func]
println[inputForm[eq]]
g = new graphics
// Change the last number to vary the resolution. This is the number
// of doublings, so if the number is 10 we have 2^10=1024 doublings for
// a resolution of 1024x1024.
testRect[-10,10,-10,10, g, eq, 10]
g.show[]
g.write["graph2.png",1024,1024]
}
// Recursive function to test an interval containing the specified bounds.
// If no possible solution exists, the recursion halts. If a possible solution
// exists, this breaks it down into 4 sub-rectangles and tests each of them
// recursively. level is the maximum number of levels to split, so the total
// resolution of the final graph will be 2^level.
testRect[x1, x2, y1, y2, g, eq, level] :=
{
nextLevel = level - 1
x = new interval[x1, x2]
y = new interval[y1, y2]
// Test the rectangle. If it possibly contains solutions, recursively
// subdivide.
res = eval[eq]
if res or res==undef
{
if (nextLevel >= 0)
{
cx = (x1 + x2)/2
cy = (y1 + y2)/2
testRect[x1, cx, y1, cy, g, eq, nextLevel]
testRect[cx, x2, y1, cy, g, eq, nextLevel]
testRect[x1, cx, cy, y2, g, eq, nextLevel]
testRect[cx, x2, cy, y2, g, eq, nextLevel]
} else
if (res) // Valid point
g.fillRectSides[x1, -y1, x2, -y2]
else
{
// Error in evaluating point
g.color[1,0,0]
g.fillRectSides[x1, -y1, x2, -y2]
g.color[0,0,0]
}
}
}
Download or view simplegraph3.frink in plain text format
This is a program written in the programming language Frink.
For more information, view the Frink
Documentation or see More Sample Frink Programs.
Alan Eliasen was born 20194 days, 8 hours, 31 minutes ago.