# 3.4 Java3003: drawing graphs with turtles and pixels  (Page 8/13)

 Page 8 / 13

The value returned from the Math.sqrt method can be considered to be either positive or negative. Only the positivevalue is returned by this method. When the returned value is considered to be positive and the results are plotted, one-half of a circle is displayed as shownby the BLUE line in Figure 10 . Similarly, when the returned value is considered to be negative and the results are plotted, the other half of the circle isdisplayed as shown by the GREEN line in Figure 10 .

Listing 10 . The method named function for Circle01. ```double function(double rVal,double xVal){ double yVal = Math.sqrt(rVal*rVal - xVal*xVal + 0.0000000001);return yVal; }//end function```

If the expression passed to the sqrt method is negative, the value returned by that method will not be valid. Because the computations inthis program are performed as type double , and because all floating point computations are only estimates of the truth, the computed differencebetween the radius squared and the x-value squared can actually be an extremely small negative value when it should be zero. A small positive fudge factor wasadded to prevent that value from going negative due to small floating point computational errors. (This sort of thing is often required when doing a lot of floating point computations. There are various ways to do it and there may bebetter ways than the one used here.)

## Draw half the circle in BLUE

The code in Listing 11 draws the BLUE half of the circle shown in Figure 10 .

Listing 11 . Draw half the circle in BLUE. ```for(int cnt=0; cnt<=100;cnt++,xVal += xInc){ //Get a y-value for the given x-value.yVal = function(rVal,xVal); //Apply the offsets and scale the resultscol = (int)((xOff+xVal)*xScale); row = (int)((yOff+yVal)*yScale);//Move to the first point without drawing a line because the// pen is not down. Translate the origin to the center in the // process.turtle.moveTo(col + world.getWidth()/2, row + world.getHeight()/2);//Lower the pen in order to draw a line from each point to the // next point.turtle.penDown(); }//end for loop```

Having initialized xVal and xInc on the basis of the radius in Listing 9 , the code in Listing 11 is essentially the same as the code in the earlier programs in this lesson.

## Draw the other half of the circle in GREEN

The code that draws the GREEN half of the circle is shown in Listing 18 . It is essentially the same as the code in Listing 10 except that the sign on yVal is flipped from positive to negative as discussed above .

## Different line width

One other difference that I haven't mentioned yet is trivial but interesting. You may have noticed that the line width in Figure 10 is about twice that in Figure 9 . I purposely did that to illustrate that one of the useful features of graphing functions with a turtle is that you can control the width of the line.The importance of that capability will become apparent in the next section.

That concludes the interesting differences between this program and the previous programs.

where we get a research paper on Nano chemistry....?
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!