Program: InterpX3
By: Ben Axelrod   


     What is interpolation?  2D interpolation takes two points and draws a 
line through them.  Then it takes the X value you gave it (which is usually 
between these points but does not have to be) and uses this imaginary line 
to find the Y value there.  You could also give it Y to get X.  It doesnt 
mater.  What usually happens when you have problems with 3 variables, one is 
usually constant.  This way you can just do a normal 2D interpolation 
holding the other constant.  However, you might have to work in the (x,z) or 
another weird plane.  But the numbers will work out, and you will get the 
right answer. 

     3Dimensional interpolation is just three, 2D interpolations.  Of 
course, the 4 points that you give it have to be squared to the X and Y 
axes.  (They have to make a rectangle, not a diamond)  That was the reason I 
wrote this program.  What if the information you had wasnt so nice?  This 
program uses the methods in Interp2X, which is basically the Pythagorean 
theorem, and applies it a couple of times.  Now you can enter your points in 
a diamond and it will work.

     Here is a bad drawing of what you can have.  The *s are the 4 data 
points that you do not have to enter as numbered.  The O is The Point in 
question.  It does not have to be in side the four points you have, but it 
is best.  Notice how the 4 points do not have to be squared.  That is the 
power of this program.


y |                      
  |                       *2 
  |  
  |            
  |        *1 
 ---              O  
  |
  |
  |
  |    *3             
  |                   *4
  |     
 -|---------------|---------
                           x 


     I have 3 other interpolation programs that you should take a look at.  
If you have any questions or comments, please email me at: bmaxelro@syr.edu
