Help need on math java program

[zidangus]

Hi I am trying to write a java program that lets me evaluate the value of x over the range x=0 to100, for the function y=a*(x*8))+b*((x*8)^-0.5))+c and then print the values of y into a file. However the attempt I made below does not work can someone help me out and show me where I am going wrong and what to do to make the code work.

public class javatest {

public static void main(String[] args) {

// Stream to write file
FileOutputStream fout;

try
{
// Open an output stream
fout = new FileOutputStream ("output.txt");

double a = 5;
double b = 10;
double c = 15;
double y;
double x;
y=(a*(x*8))((b)*Math.pow((x*8)),-0.5)c;


// for x returns y for 100 channels.
for (x=0; x < 100; x+) {
System.out.println(
"The value of y is " y;

// Print a line of text
new PrintStream(fout).println (" The value of y is" y;);

// Close our output stream
fout.close();

}

}

}

[Fubarable]

Please BeForthrightWhenCrossPostingToOtherSites

[Norm]

attempt I made below does not work

Please explain.

[zidangus]

Ok I am knew to programming so forgive me if I dont know the "rules".
The other forums I asked this question were
Java Programming - Help needed using math in java
and
Help need on math java program - Java Programming Forums
When I say it does not work I mean it does not compile.
I have went through all the errors and I am left with the compiler complaining about using "to" and "catch"

[Norm]

it does not compile.

Please copy and paste the full text of the error messages here.

[al_Marshy_1981]

Ok I am knew to programming so forgive me if I dont know the "rules".
The other forums I asked this question were
Java Programming - Help needed using math in java
and
Help need on math java program - Java Programming Forums
When I say it does not work I mean it does not compile.
I have went through all the errors and I am left with the compiler complaining about using "to" and "catch"

you probably mean try and catch???

You have a try clause, it needs a to be completed with a catch clause.

e.g.

try{
int sumVariable=10
}
catch(Exception e)
{
e.printstacktrace();
}

catch comes after the closing brace of the try closing brace.

[zidangus]

I have tried to write the code again. But I still cannot get it to print out every value of y for all values of x between 0 and 100. The new code is below. By the way it compiles but only prints out the value of y for x =101 ?.

//Evaluate function
import java.lang.*;
import javax.swing.*;
import java.text.*;
import java.io.*;

public class jurofunction
{                                                                      //begin class scope
//get user input for the variables
public static void main(String arg[])
{                                                                     // begin main method scope

JOptionPane.showMessageDialog(null, " The program calculates the value of y for a function of the form y = ax + bx ^-0.5 + c");
// get input from the user for the variables a b  and offset

 double a =
      validateDouble("Please enter the value of a", "Input a");                      // ask the user for values of a b and offset and store them in method which validates the input see below

    double b =
      validateDouble("Please enter the value of b", "Input b");
      
     double c =
      validateDouble("Please enter the value of offset", "Input c");
      int x;
      double y=0;

for (x=0; x<=100; x++)

y = (a*(x*8)) + (b*Math.pow((x*8),-0.5))+c

//  These next three lines allow the answer y to be rounded to 3 decimal places
NumberFormat nf = NumberFormat.getNumberInstance();     
nf.setMinimumFractionDigits(5);
nf.setMaximumFractionDigits(5);
// Displays value of y to 5 decimalplaces
JOptionPane.showMessageDialog(null, " The value of y is " + nf.format(y)); 
//Display text showing thanks for using the program 
JOptionPane.showMessageDialog(null, " Thank you for using the program"); 
");

//Create stream to write file to
FileOutputStream fiout;
try
{                                                                         //begining of try block
//open an output stream
fiout = new FileOutputStream ("The-value-of-y.txt");
// print to ouput file
new PrintStream(fiout).println("Thanks for using the program.");
new PrintStream(fiout).println("With a =" + nf.format(a));
new PrintStream(fiout).println("With b =" + nf.format(b));
new PrintStream(fiout).println("With offset =" + nf.format(c));
new PrintStream(fiout).println("With x =" + nf.format(x));
new PrintStream(fiout).println("The value of y is " + nf.format(y));
// close the output stream
fiout.close();
}                                                                        // end of try block
//Catch any errors
catch (IOException e)                                   
{                                                                       //begining of catch block
System.err.println ("Unable to write o file ");
System.exit(-1);
}                                                                      // end of catch block
}                                                                      //end of main method scope

                                                                    
      
public static double validateDouble(String prompt, String titleBar)                            // begining of method to stop user invalid input 
  {
    boolean inputIsValid = false;
    String inputString = null;
    double input = 0.0;

    do {
      inputString =
        JOptionPane.showInputDialog(null, prompt, titleBar, JOptionPane.QUESTION_MESSAGE);

      // Input is valid if the user typed something
      inputIsValid = (inputString != null);

      // If the input is valid so far, attempt to convert it
      if (inputIsValid) {
        // Convert inputString to type double
        try {
          input = Double.parseDouble(inputString);                                      // here it ensures only double values can be accepted.
        }
        catch (NumberFormatException ex) {
          JOptionPane.showMessageDialog(null,"Invalid input value.","Error: Invalid Input",JOptionPane.ERROR_MESSAGE);

          // Set flag to false
          inputIsValid = false;
        }
        
          }
    }
    while (!inputIsValid);    // i.e. inputIsValid == false

    return input;
  }
  }	                                                          // end of class scope

Any ideas as to where i am going wrong here ?

[Norm]

for (x=0; x<=100; x++)

Should this for have { and } following it enclosing more than 1 statement?

[zidangus]

Yes sorry it should have { }. The code compiles however it only prints out one value of y and thats at x=101. I want it to print out all values of y for x between 0 and 100.
Any suggestions on how I can get it to do this ?

[arun9683]

Try with the below modification

for (x=0; x<=100; x++)
{

y = (a*(x*8)) + (b*Math.pow((x*8),-0.5))+c

// These next three lines allow the answer y to be rounded to 3 decimal places
NumberFormat nf = NumberFormat.getNumberInstance();
nf.setMinimumFractionDigits(5);
nf.setMaximumFractionDigits(5);
// Displays value of y to 5 decimalplaces
JOptionPane.showMessageDialog(null, " The value of y is " + nf.format(y));
//Display text showing thanks for using the program
JOptionPane.showMessageDialog(null, " Thank you for using the program");
");

//Create stream to write file to
FileOutputStream fiout;
try
{ //begining of try block
//open an output stream
fiout = new FileOutputStream ("The-value-of-y.txt");
// print to ouput file
new PrintStream(fiout).println("Thanks for using the program.");
new PrintStream(fiout).println("With a =" + nf.format(a));
new PrintStream(fiout).println("With b =" + nf.format(b));
new PrintStream(fiout).println("With offset =" + nf.format(c));
new PrintStream(fiout).println("With x =" + nf.format(x));
new PrintStream(fiout).println("The value of y is " + nf.format(y));
// close the output stream
fiout.close();
} // end of try block
//Catch any errors
catch (IOException e)
{ //begining of catch block
System.err.println ("Unable to write o file ");
System.exit(-1);
}

}// for closed

[Norm]

Please use code tags when posting code.

[JosAH]

I think that the OP has the fundamental misunderstanding that if a variable y functionally depends on a variable x:

y= f(x);

and if x changes that 'automagically' y changes accordingly. In Java (and a whole lot of other programming languages) it doesn't; i.e. you have to re-evaluate y again for new values of x; so that would be:

for (int x= 0; x < 100; x++) { // changing values of x
   y=f(x); // re-evaluate y because it depends on x
   ...
}

kind regards,

Jos

[zidangus]

Thanks JosAH, I tried your advice and it does not compile, am I putting your code in the right place ?

public class jurofunction3
{                                                                      //begin class scope
//get user input for the variables
public static void main(String arg[])
{                                                                     // begin main method scope

JOptionPane.showMessageDialog(null, " The program calculates the value of y for 3rd order polynominals of the form y = ax + bx ^-0.5 + c");
// get input from the user for the variables x z and h

 double a =
      validateDouble("Please enter the value of a", "Input a");                      // ask the user for values of a b and offset and store them in method which validates the input see below

    double b =
      validateDouble("Please enter the value of b", "Input b");
      
     double c =
      validateDouble("Please enter the value of offset", "Input c");
     int x;
     double y;
    double f(x);
    
 
    y= (a*(x*8)) + (b*Math.pow((x*8),-0.5))+c;

for (x= 0; x < 100; x++) { // changing values of x
    y=f(x); // re-evaluate y because it depends on x
   
}

}

compile errors
jurofunction3.java:26: cannot find symbol
symbol : method f(int)
location: class jurofunction3
double y=f(x)=0;
^
jurofunction3.java:30: cannot find symbol
symbol : method f(int)
location: class jurofunction3
y=f(x); // re-evaluate y because it depends on x
^
jurofunction3.java:31: cannot find symbol
symbol : method f(int)
location: class jurofunction3
f(x) = (a*(x*8)) + (b*Math.pow((x*8),-0.5))+c;
^
3 errors

[Norm]

f(x) was pseudo code, not java code.

[JosAH]

Thanks JosAH, I tried your advice and it does not compile, am I putting your code in the right place ?

public class jurofunction3
{                                                                      //begin class scope
//get user input for the variables
public static void main(String arg[])
{                                                                     // begin main method scope

JOptionPane.showMessageDialog(null, " The program calculates the value of y for 3rd order polynominals of the form y = ax + bx ^-0.5 + c");
// get input from the user for the variables x z and h

 double a =
      validateDouble("Please enter the value of a", "Input a");                      // ask the user for values of a b and offset and store them in method which validates the input see below

    double b =
      validateDouble("Please enter the value of b", "Input b");
      
     double c =
      validateDouble("Please enter the value of offset", "Input c");
     int x;
     double y;
    double f(x);
    
 
    y= (a*(x*8)) + (b*Math.pow((x*8),-0.5))+c;

for (x= 0; x < 100; x++) { // changing values of x
    y=f(x); // re-evaluate y because it depends on x
   
}

}

compile errors
jurofunction3.java:26: cannot find symbol
symbol : method f(int)
location: class jurofunction3
double y=f(x)=0;
^
jurofunction3.java:30: cannot find symbol
symbol : method f(int)
location: class jurofunction3
y=f(x); // re-evaluate y because it depends on x
^
jurofunction3.java:31: cannot find symbol
symbol : method f(int)
location: class jurofunction3
f(x) = (a*(x*8)) + (b*Math.pow((x*8),-0.5))+c;
^
3 errors

Look what you did: you introduced an 'f' without telling Java what that 'f' means. I just used that 'f' as any function so that y would be functionally dependent of x, so: y= f(x). Java, and all other programming languages, is way too stupid to understand your intentions (although I doubt you had any intentions at all except getting rid of this bloody program ;-) If you want 'f' to be understood by Java you have to define 'f' as a function, like so:

private static double f(double x) { 
    return (a*(x*8)) + (b*Math.pow((x*8),-0.5))+c;
}

and a, b and c have to be defined somewhere where 'f' can find them. For now forget this construct and forget about my 'f'; it was just a matter of speech. Instead of writing y= f(x); write this:

y= (a*(x*8)) + (b*Math.pow((x*8),-0.5))+c;

in the body of your loop.

kind regards,

Jos

[Fubarable]

I already mentioned his creating a method in his cross-post yesterday, but he never responded to me or to many other responses in that thread... which is one reason I hate cross-posters....

[JosAH]

I already mentioned his creating a method in his cross-post yesterday, but he never responded to me or to many other responses in that thread... which is one reason I hate cross-posters....

Ditto here; it made me think not to post code-formatted code blocks anymore because that's what most posters just copy and paste without reading the rest of the reply. See above: blindly copying pseudo code and complaining when it doesn't work. I am amazed that still some progress is being made in the world; it won't take long before it all comes to a standstill.

kind regards,

Jos

[zidangus]

I would just like to know how can I get it to print in the output file all values of Y for each value of X in the loop. i have tried your suggestions and they do not compile. I am getting a headache :confused:

[Norm]

they do not compile

You'll have to post the errors for anyone to help.

I am getting a headache

You're not alone.

[JosAH]

I would just like to know how can I get it to print in the output file all values of Y for each value of X in the loop. i have tried your suggestions and they do not compile. I am getting a headache :confused:

Sigh, have a look at this:

int x;
double y;
double a, b, c;

// first set values for a, b and c here ...

for (x= 0; x < 100; x++) {
   y= (a*(x*8)) + (b*Math.pow((x*8),-0.5))+c;
   System.out.println(x+" "+y);
}