Root with Bigdecimal

Question

I’m racking my brain to turn a root into a code.

I know it works kind of like this:

Math.pow(625, (1.0/4)) = raiz 4ª de 625 = 5

My headache is that my dice are BigDecimals

Sting prazoIn = idtText.getText();
BigDecimal prazo = new BigDecimal(prazoIn);

String valorIn = idtText.getText2();
BigDecimal valor = new BigDecimal(valorIn);


BigDecimal umPonto = new BigDecimal(1.0);

//Não sei como fazer com valores BigDecimais
BigDecimal raiz = Math.pow(valor, (umPonto.divide(prazo);

Answer 1

Unfortunately you don’t have a solution ready. If converting to another type is a valid option, then you have no reason to use BigDecimal. The conversion will cause loss of value, and worse, so that often naive tests will not detect.

Since Java does not provide anything ready you have to do a function of your own. There’s one in the O.R.:

public static BigDecimal powerBig(BigDecimal base, BigDecimal exponent) {
    BigDecimal ans = new BigDecimal(1.0);
    BigDecimal k = new BigDecimal(1.0);
    BigDecimal t = new BigDecimal(-1.0);
    BigDecimal no = new BigDecimal(0.0);
    if (exponent != no) {
        BigDecimal absExponent =  exponent.signum() > 0 ? exponent : t.multiply(exponent);
        while (absExponent.signum() > 0){
            ans =ans.multiply(base);
            absExponent = absExponent.subtract(BigDecimal.ONE);
        }
        if (exponent.signum() < 0) {
            // For negative exponent, must invert
            ans = k.divide(ans);
        }
    } else {
        // exponent is 0
        ans = k;
    }
    return ans;
}

I put in the Github for future reference.

Also has square root option.

Have libraries ready:

• Cornell University
• Suanshu

Answer 2

Do it this way, depending on the size of the accuracy you need, solve..

public BigDecimal raiz() {
    return new BigDecimal(Math.pow(new BigDecimal(1.172544).floatValue(), (1.0 / 7)));
}

//retorno 1.022999903326536230707688446273095905780792236328125