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cbrt

Cube root.

SYNOPSIS:

double x, y, cbrt();
y = cbrt(x);

DESCRIPTION:
Returns the cube root of the argument, which could be negative. Range reduction involves determining the power of 2 of the argument. A polynomial of degree 2 applied to the mantissa, and multiplication by the cube root of 1, 2, or 4 approximates the root to within about 0.1%. Then Newton's iteration is used three times to converge to an accurate result.

ACCURACY:
                      Relative error:
arithmetic   domain     # trials      peak         rms
    DEC        -10,10     200000      1.8e-17     6.2e-18
    IEEE       0,1e308     30000      1.5e-16     5.0e-17

JavaScript:

//
//Plot of y = 3vx.
//

function plotYforX(x1, x2)
{
for(var x = x1; x <= x2; x++)
{
var y = cephes.cbrt(x);
Session.Output("plot of x for " + x + " gives y of " + y);
}
}

function main()
{
plotYforX(-1,6);
}
main();