问题描述:

i am trying to not import the math class to use but i am still trying to estimate the constant "e". it is said e= 1+(1/1!)+(1/2!)+(1/3!)+(1/4!)+(1/5!)+.....

these are what i have int at the top

String userInput;

int uIp; // this converts the string into int type

double e = 2;

then i ask some questions then i check to see not zero to exit and non negative to continue

While(uIp >0){

final int endTheLoop = 15;

int factorialNumber = 1;

double e2TheUserInput=0;

for(int i = 2; i < endTheLoop; i++){

for(int j = 1; j < i; j++){

factorialNumber = ((i - 1) * factorialNumber);

}

e = (1/factorialNumber) + e;

e2TheUserInput = Math.pow(e,uIp);

}

}

网友答案:

You are doing integer division(but e is a double right?):

e = (1/factorialNumber) + e;

Correct that to:

e = (1.0/(double)factorialNumber) + e;

It was counting all the loops, but changes are zero according to the integer division. :)

e= 2+(0)+(0)+(0)+(0)+.....

网友答案:

I am not sure what your code is trying to do but if you want to compute exp(x) this is how I would do it.

public static void main(String... args) {
    for (int i = -4; i <= 4; i++)
        System.out.println(i + ": " + exp(i) + " cf " + Math.exp(i));
}

private static double exp(double d) {
    if (d < 0)
        return 1 / exp(-d);
    double e = 1, term = 1;
    for (int i = 1; i < 20 || term > e * 1e-16; i++) {
        term *= d / i;
        e += term;
    }
    return e;
}

For large exponents, it more efficient to evaluate the integral powers without using a taylor series.

public static final double E = 2.7182818284590452354;

private static double exp(double d) {
    if (d < 0)
        return 1 / exp(-d);
    long num = (long) d;
    double numE = 1;
    double mult = E;
    while (num > 0) {
        if ((num & 1) != 0)
            numE *= mult;
        num >>>= 1;
        mult *= mult;
    }
    double fract = d - (long) d;
    double fractE = 1, term = 1;
    for (int i = 1; i < 20; i++) {
        term *= fract / i;
        fractE += term;
    }
    return numE * fractE;
}
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