Java

The problem with using Java's maths.cos()

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dandan

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Re: The problem with using Java's maths.cos()

#11

Jan 25th, 2006

System.out.println(Math.cos(Math.toRadians(90)));
System.out.println(Math.cos(Math.toRadians(270)));

gives

6.123233995736766E-17
-1.8369701987210297E-16

good enough for most purposes.

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jwenting

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Re: The problem with using Java's maths.cos()

#12

Jan 25th, 2006

P.S. I've done a small test and Math.cos(x) yields correct results which are in line with the ones the Windows calculator produces down to their last decimal place (when the latter is set to radians of course).

The following will print the cosine of every angle between 0 and 2 pi:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
            double rad = 0.0;
            double interval = 0.1;
 
            while (rad < 2*Math.PI) {
                System.out.print(rad);
                System.out.print(" -> ");
                System.out.println(Math.cos(rad));
                rad += interval;
            }
            double rad = 0.0;
            double interval = 0.1;
            
            while (rad < 2*Math.PI) {
                System.out.print(rad);
                System.out.print(" -> ");
                System.out.println(Math.cos(rad));
                rad += interval;
            }

Note that normally you'd format the output to make it look nicer...

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LiBOC

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Re: The problem with using Java's maths.cos()

#13

Jan 25th, 2006

Yes, I got that answer too. But I thought 90 and 270 should yield a 0?

That is the thing I am talking about. Why would Cos90 and Cos270 in math.cos() be not 0?

So sorry, for the timebeing, my sourcecode is not with me. I can't post it here.

However my objective is to:

1)Calculate the cosine angle of x
WITHOUT using the math.cos()

2)It allows students or users to type in their desired
Angle in Degrees and Number of Terms to calculate.
More number of terms means more accurate calculation.

3)And error handling which I can handle.

CONCLUSION : The ultimate questions is,
1) Why math.cos() for 90 and 270 is not 0.
2) How do I not use math.cos() to calculate cosine.

I will be posting the cosine maths formula soon. Thank you!

Hope I am not confusing anyone! a BIG thank you for your overwhelming responses!

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Originally Posted by dandan

System.out.println(Math.cos(Math.toRadians(90)));
System.out.println(Math.cos(Math.toRadians(270)));

gives

6.123233995736766E-17
-1.8369701987210297E-16

good enough for most purposes.

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jwenting

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duckman

Re: The problem with using Java's maths.cos()

#14

Jan 26th, 2006

Because, as has been mentioned many times already, Math.cos (and Math.sin and others) are NOT going to convert degrees to radians for you.

Maybe you should learn about trigonometric calculations first before trying to use them in your software, maybe then things might become clear(er) to you.

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iamthwee

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Re: The problem with using Java's maths.cos()

#15

Jan 26th, 2006

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So sorry, for the timebeing, my sourcecode is not with me. I can't post it here.

However my objective is to:

1)Calculate the cosine angle of x
WITHOUT using the math.cos()

2)It allows students or users to type in their desired
Angle in Degrees and Number of Terms to calculate.
More number of terms means more accurate calculation.

Oh i c wat u r trying to do now. Ur simply trying to evaluate the cos(x) using taylor's series?

http://www.maths.abdn.ac.uk/~igc/tch...pl/node59.html

And that's wat u meant by adding all the terms. Silly me?

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Re: The problem with using Java's maths.cos()

#16

Jan 26th, 2006

The best thing to do is draw a triangle if you're confused and the unit circle doesn't help. The only problem with using a triangle is you'll have to use some logic, because you'll start with 2 unknowns (from what I remember).

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LiBOC

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Re: The problem with using Java's maths.cos()

#17

Jan 26th, 2006

yes.. with series...

Regarding to converting radians.. i had already converted right?

if("Calculate".equals(actionCommand))
d= Math.cos(Math.toRadians(d));

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Originally Posted by iamthwee

Oh i c wat u r trying to do now. Ur simply trying to evaluate the cos(x) using taylor's series?

http://www.maths.abdn.ac.uk/~igc/tch...pl/node59.html

And that's wat u meant by adding all the terms. Silly me?

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LiBOC

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Re: The problem with using Java's maths.cos()

#18

Jan 26th, 2006

This is the maths formula I am trying to get students to calculate using Java. Thank you.

http://img.photobucket.com/albums/v6...i/DSC00066.jpg

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iamthwee

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Re: The problem with using Java's maths.cos()

#19

Jan 26th, 2006

U no you can use [.tex] tags to write formulae. Which is why cscgal made incorporated them into daniweb!

${\cos x = 1 - \frac{x^2}{2!} + \frac{x^4}{4!} - \frac{x^6}{6!}+ \frac{x^8}{8!} - \cdots}$

But yes, that would be simple enuff to do in java.

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jwenting

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duckman

Re: The problem with using Java's maths.cos()

#20

Jan 26th, 2006

simple enough indeed, easy mathematical sequence.
Program as a loop, several ways to determine whether to add or subtract.

Trickiest is how to determine when to terminate the loop, unless you're using a fixed number of iterations.