Java for-loop问题 [英] java for-loop problem
问题描述
public static void main(String [] args)
{
double totalS = 0.0;
int count = 0;
(double i = 0; i <4; i + = 0.4)
{
count ++;
totalS + = Sfunction(i,count);
System.out.println(count ++ i ++ totalS);
public static double Sfunction(double f1,int count)
{
double value;
if(f1 == 0.0 || f1 == 4.0)
value = Math.cos(Math.sqrt(f1));
else if((count count 2)== 1)
value = 2 * Math.cos(Math.sqrt(f1));
else
value = 4 * Math.cos(Math.sqrt(f1));
返回值;
$ / code $ / pre
$ b $我得到的输出:
1 0.0 1.0
2 0.4 4.226313639540303
3 0.8 5.478244888601832
4 1.2000000000000002 7.30884788480188
5 1.6 7.911122809972827
6 2.0 8.534897589034324
7 2.4 8.578100205110182
8 2.8 8.168723348285942
9 3.1999999999999997 7.736055200662704
10 3.5999999999999996 6.452869366954546
11 3.9999999999999996 5.620575693860261
pre
解决方案每次循环时,都会在0.4的不精确加法中加入错误。 p>
取而代之的是,使用循环计数器的整数值,并缩放以获得更好的近似值:
<$ (int count = 0; count <10; ++ count){
final double i = 0.4 * count; p $ p>
System.out.println((count + 1)++ i);
$ b 这不会消除浮点错误,但这意味着它不是在每个迭代增加。要从输出中删除错误,请将输出格式化为合理的小数位数:
for(int count = 0; count <10; ++ count){
final double i = 0.4 * count;
System.out.printf(%2d%.1f\\\
,(count + 1),i);
}
I am making a Java program to calculate Simpson's rule for integrals. Here is the code I have. Notice the second column of numbers in the output values of count == 4,9,10,11. They are not numbers that I need, they do not follow the pattern. I need these numbers to be accurate. What is going on and how can I fix it?
public static void main(String[] args)
{
double totalS = 0.0;
int count = 0;
for(double i=0; i< 4; i += 0.4 )
{
count++;
totalS += Sfunction(i, count);
System.out.println(count + " " + i + " " + totalS);
}
}
public static double Sfunction(double f1, int count)
{
double value;
if (f1 == 0.0 || f1 == 4.0)
value = Math.cos(Math.sqrt(f1));
else if ((count % 2) == 1)
value = 2 * Math.cos(Math.sqrt(f1));
else
value = 4 * Math.cos(Math.sqrt(f1));
return value;
}
I get the output of:
1 0.0 1.0
2 0.4 4.226313639540303
3 0.8 5.478244888601832
4 1.2000000000000002 7.30884788480188
5 1.6 7.911122809972827
6 2.0 8.534897589034324
7 2.4 8.578100205110182
8 2.8 8.168723348285942
9 3.1999999999999997 7.736055200662704
10 3.5999999999999996 6.452869366954546
11 3.9999999999999996 5.620575693860261
解决方案 Each time you go round your loop, you are compounding the error in the inexact addition of 0.4 to i.
Instead, use an integral value for the loop counter, and scale that to get a better approximation to the values:
for ( int count = 0; count < 10; ++count ) {
final double i = 0.4 * count;
System.out.println ( ( count + 1 ) + " " + i );
}
This will not eliminate the floating point error, but it will mean it is not increasing at each iteration. To remove the error from the output, format the output to a reasonable number of decimal places:
for ( int count = 0; count < 10; ++count ) {
final double i = 0.4 * count;
System.out.printf ( "%2d %.1f\n", ( count + 1 ), i );
}
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