atan

/*
 *  call-seq:
 *     Math.atan(x)    => float
 *  
 *  Computes the arc tangent of <i>x</i>. Returns -{PI/2} .. {PI/2}.
 */

static VALUE
math_atan(obj, x)
    VALUE obj, x;
{
    Need_Float(x);
    return rb_float_new(atan(RFLOAT(x)->value));
}