java 如何解决java中的cos 90问题？
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how to solve cos 90 problem in java?
提问by David King
I have some problems with calculating cosinus 90 in Java using Math.cos function :
我在使用 Math.cos 函数在 Java 中计算余弦 90 时遇到了一些问题：
public class calc{
private double x;
private double y;
public calc(double x,double y){
this.x=x;
this.y=y;
}
public void print(double theta){
x = x*Math.cos(theta);
y = y*Math.sin(theta);
System.out.println("cos 90 : "+x);
System.out.println("sin 90 : "+y);
}
public static void main(String[]args){
calc p = new calc(3,4);
p.print(Math.toRadians(90));
}
}
}
When I calculate cos90 or cos270, it gives me absurb values. It should be 0. I tested with 91 or 271, gives a near 0 which is correct.
当我计算 cos90 或 cos270 时，它给了我荒谬的值。它应该是 0。我用 91 或 271 进行了测试，结果接近 0，这是正确的。
what should I do to make the output of cos 90 = 0? so, it makes the output x = 0 and y = 4.
我该怎么做才能使 cos 90 = 0 的输出？因此，它使输出 x = 0 和 y = 4。
Thankful for advice
感谢您的建议
采纳答案by Ignacio Vazquez-Abrams
What you're getting is most likely very, very small numbers, which are being displayed in exponential notation. The reason you're getting them is because pi/2 is not exactly representable in IEEE 754 notation, so there's no way to get the exact cosine of 90/270 degrees.
您得到的很可能是非常非常小的数字，它们以指数表示法显示。你得到它们的原因是因为 pi/2 不能完全用 IEEE 754 表示法表示，所以没有办法得到 90/270 度的精确余弦。
回答by MicSim
Just run your source and it returns:
只需运行您的源代码，它就会返回：
cos 90 : 1.8369701987210297E-16
sin 90 : 4.0
That's absolutely correct. The first value is nearly 0. The second is 4 as expected.
这是完全正确的。第一个值接近于 0。第二个是 4，正如预期的那样。
3 * cos(90°) = 3 * 0 = 0
3 * cos(90°) = 3 * 0 = 0
Here you have to read the Math.toRadians()documentation which says:
在这里，您必须阅读Math.toRadians()文档，其中说：
Converts an angle measured in degrees to an approximately equivalent angle measured in radians. The conversion from degrees to radians is generally inexact.
将以度为单位的角度转换为以弧度为单位的近似等效的角度。从度数到弧度的转换通常是不准确的。
Update:You can use for example the MathUtils.round()method from the Apache Commons repository and round the output to say 8 decimals, like this:
更新：例如，您可以使用Apache Commons 存储库中的MathUtils.round()方法并将输出四舍五入为 8 位小数，如下所示：
System.out.println("cos 90 : " + MathUtils.round(x, 8));
That will give you:
这会给你：
cos 90 : 0.0
sin 90 : 4.0
回答by Eng.Fouad
Try this:
试试这个：
public class calc
{
private double x;
private double y;
public calc(double x,double y)
{
this.x=x;
this.y=y;
}
public void print(double theta)
{
if( ((Math.toDegrees(theta) / 90) % 2) == 1)
{
x = x*0;
y = y*Math.sin(theta);
}
else if( ((Math.toDegrees(theta) / 90) % 2) == 0)
{
x = x*Math.cos(theta);
y = y*0;
}
else
{
x = x*Math.cos(theta);
y = y*Math.sin(theta);
}
System.out.println("cos 90 : "+x);
System.out.println("sin 90 : "+y);
}
public static void main(String[]args)
{
calc p = new calc(3,4);
p.print(Math.toRadians(90));
}
}
