Function Program

[d0ugg]

Hello,

I need to write a Function program that will check if a function is valid or not and also if the function is onto as well.
Kind of getting started right now, so any ideas will be great.

Thank you!

[Nepomuk]

Hello,

I need to write a Function program that will check if a function is valid or not and also if the function is onto as well.
Kind of getting started right now, so any ideas will be great.

Thank you!

In what form will the function, which should be checked, be given to the checker function and what type of functions should they be? Should the syntax be checked or the result? Can the functions have side effects and if so, should those be checked too? We'll need some more information, to be able to help you.

Greetings,
Nepomuk

[d0ugg]

Hi,

Thanks for the quick answer.

For example,

Given the function f, from {1 2 3 4 5}, to itself. Than I have to check if it is a one-to-one function and also if it is a onto function.
The program will test the following functions:
f(1) = 4
f(2) = 3
f(3) = 1
f(5) = 2

Thank you

[Nepomuk]

Hi,

Thanks for the quick answer.

For example,

Given the function f, from {1 2 3 4 5}, to itself. Than I have to check if it is a one-to-one function and also if it is a onto function.
The program will test the following functions:
f(1) = 4
f(2) = 3
f(3) = 1
f(5) = 2

Thank you

OK, you're talking about a mathematical function f: X -> Y, where X = {1,2,3,4,5} and you want to know, if its injective and/or surjective?

I guess, it depends. If you only have relatively small sets (X and Y), you could use a for-loop to check every single value, create a set from the results and check, if the elements are equal or whatever you want to know. If however you have a big set (e.g. a set with infinite elements), you'll have to somehow code a method, which will prove or disprove that the given function is one-to-one/onto.

I guess, these sites will help:
Proving Functions are One-to-One
Proving Functions are Onto
Thank's to Google for those. :-)

Greetings,
Nepomuk

[d0ugg]

Okay,

I like the idea of the for loop.

Thank you,

Doug

[d0ugg]

Hey,

So I started the code, and I'm getting 2 errors from the compile that I can't figure it out..
The errors are in those lines

 
if (testA == 1 || testA == 2 || testA== 3 || testA == 4 || testA == 5)
        {
            if(testB == 2 || testB == 3 || testB = 4 || testB == 5)
            {
                if(testC == 3 || testC == 4 || testC == 5)
                {
                    if(testD== 4 || testD ==5)
                    {
                        if(testE ==5)
                                                {
    System.out.print("\nThat's really good");
                                               }
                    }
                }
            }                
        }
 

Well I guess I can't do that, the compile says:

function.java:55: operator || cannot be applied to boolean,int
if(testB == 2 || testB == 3 || testB = 4 || testB == 5)


Any ideas?

Thank you,

Doug

[r035198x]

Hey,

So I started the code, and I'm getting 2 errors from the compile that I can't figure it out..
The errors are in those lines

 
if (testA == 1 || testA == 2 || testA== 3 || testA == 4 || testA == 5)
        {
            if(testB == 2 || testB == 3 || testB = 4 || testB == 5)
            {
                if(testC == 3 || testC == 4 || testC == 5)
                {
                    if(testD== 4 || testD ==5)
                    {
                        if(testE ==5)
                                                {
    System.out.print("\nThat's really good");
                                               }
                    }
                }
            }                
        }
 

Well I guess I can't do that, the compile says:

function.java:55: operator || cannot be applied to boolean,int
if(testB == 2 || testB == 3 || testB = 4 || testB == 5)


Any ideas?

Thank you,

Doug

Ever heard of a switch?

[Nepomuk]

Hey,

So I started the code, and I'm getting 2 errors from the compile that I can't figure it out..
The errors are in those lines

 
if (testA == 1 || testA == 2 || testA== 3 || testA == 4 || testA == 5)
        {
            if(testB == 2 || testB == 3 || testB = 4 || testB == 5)
            {
                if(testC == 3 || testC == 4 || testC == 5)
                {
                    if(testD== 4 || testD ==5)
                    {
                        if(testE ==5)
                                                {
    System.out.print("\nThat's really good");
                                               }
                    }
                }
            }                
        }
 

Well I guess I can't do that, the compile says:

function.java:55: operator || cannot be applied to boolean,int
if(testB == 2 || testB == 3 || testB = 4 || testB == 5)


Any ideas?

Thank you,

Doug

You've left out a "=":

function.java:55: operator || cannot be applied to boolean,int
if(testB == 2 || testB == 3 || testB = 4 || testB == 5)

But as r035198x said, use switch for that part - it will be much easier.

Greetings,
Nepomuk