Example usage for org.apache.commons.math3.dfp DfpMath atan

Introduction

In this page you can find the example usage for org.apache.commons.math3.dfp DfpMath atan.

Prototype

public static Dfp atan(final Dfp a) 

Source Link

Document

computes the arc tangent of the argument Uses the typical taylor series but may reduce arguments using the following identity tan(x+y) = (tan(x) + tan(y)) / (1 - tan(x)*tan(y)) since tan(PI/8) = sqrt(2)-1, atan(x) = atan( (x - sqrt(2) + 1) / (1+x*sqrt(2) - x) + PI/8.0

Usage

From source file:org.orekit.forces.gravity.ReferenceFieldModel.java

public Dfp nonCentralPart(final AbsoluteDate date, final Vector3D position) throws OrekitException {

    int degree = provider.getMaxDegree();
    int order = provider.getMaxOrder();
    //use coefficients without caring if they are the correct type
    final RawSphericalHarmonics harmonics = raw(provider).onDate(date);

    Dfp x = dfpField.newDfp(position.getX());
    Dfp y = dfpField.newDfp(position.getY());
    Dfp z = dfpField.newDfp(position.getZ());

    Dfp rho2 = x.multiply(x).add(y.multiply(y));
    Dfp rho = rho2.sqrt();//from   ww  w .j  av a2 s  .  c o m
    Dfp r2 = rho2.add(z.multiply(z));
    Dfp r = r2.sqrt();
    Dfp aOr = dfpField.newDfp(provider.getAe()).divide(r);
    Dfp lambda = position.getX() > 0 ? dfpField.getTwo().multiply(DfpMath.atan(y.divide(rho.add(x))))
            : dfpField.getPi().subtract(dfpField.getTwo().multiply(DfpMath.atan(y.divide(rho.subtract(x)))));
    Dfp cosTheta = z.divide(r);

    Dfp value = dfpField.getZero();
    Dfp aOrN = aOr;
    for (int n = 2; n <= degree; ++n) {
        Dfp sum = dfpField.getZero();
        for (int m = 0; m <= FastMath.min(n, order); ++m) {
            double cnm = harmonics.getRawCnm(n, m);
            double snm = harmonics.getRawSnm(n, m);
            Dfp mLambda = lambda.multiply(m);
            Dfp c = DfpMath.cos(mLambda).multiply(dfpField.newDfp(cnm));
            Dfp s = DfpMath.sin(mLambda).multiply(dfpField.newDfp(snm));
            Dfp pnm = alf[n][m].value(cosTheta);
            sum = sum.add(pnm.multiply(c.add(s)));
        }
        aOrN = aOrN.multiply(aOr);
        value = value.add(aOrN.multiply(sum));
    }

    return value.multiply(dfpField.newDfp(provider.getMu())).divide(r);

}

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