cosdg

Circular cosine of angle in degrees.

SYNOPSIS:

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

DESCRIPTION:

Range reduction is into intervals of 45 degrees. Two polynomial approximating functions are employed.
Between 0 and pi/4 the cosine is approximated by:
      1 - x**2 P(x**2).
Between pi/4 and pi/2 the sine is represented as:
      x + x**3 P(x**2).

ACCURACY:
                      Relative error:
arithmetic   domain      # trials      peak         rms
    DEC      +-1000         3400       3.5e-17     9.1e-18
    IEEE     +-1000        30000       2.1e-16     5.7e-17