Math

Computes the arc cosine of x. Returns 0..PI.

Domain: [-1, 1]

Codomain: [0, PI]

Math.acos(0) == Math::PI/2 #=> true

 static VALUE
math_acos(VALUE unused_obj, VALUE x)
{
 double d;
 d = Get_Double(x);
 /* check for domain error */
 if (d < -1.0 || 1.0 < d) domain_error("acos");
 return DBL2NUM(acos(d));
}
 

Computes the inverse hyperbolic cosine of x.

Domain: [1, INFINITY)

Codomain: [0, INFINITY)

Math.acosh(1) #=> 0.0

 static VALUE
math_acosh(VALUE unused_obj, VALUE x)
{
 double d;
 d = Get_Double(x);
 /* check for domain error */
 if (d < 1.0) domain_error("acosh");
 return DBL2NUM(acosh(d));
}
 

Computes the arc sine of x. Returns -PI/2..PI/2.

Domain: [-1, -1]

Codomain: [-PI/2, PI/2]

Math.asin(1) == Math::PI/2 #=> true

 static VALUE
math_asin(VALUE unused_obj, VALUE x)
{
 double d;
 d = Get_Double(x);
 /* check for domain error */
 if (d < -1.0 || 1.0 < d) domain_error("asin");
 return DBL2NUM(asin(d));
}
 

Computes the inverse hyperbolic sine of x.

Domain: (-INFINITY, INFINITY)

Codomain: (-INFINITY, INFINITY)

Math.asinh(1) #=> 0.881373587019543

 static VALUE
math_asinh(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(asinh(Get_Double(x)));
}
 

Computes the arc tangent of x. Returns -PI/2..PI/2.

Domain: (-INFINITY, INFINITY)

Codomain: (-PI/2, PI/2)

Math.atan(0) #=> 0.0

 static VALUE
math_atan(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(atan(Get_Double(x)));
}
 

Computes the arc tangent given y and x. Returns a Float in the range -PI..PI. Return value is a angle in radians between the positive x-axis of cartesian plane and the point given by the coordinates (x, y) on it.

Domain: (-INFINITY, INFINITY)

Codomain: [-PI, PI]

Math.atan2(-0.0, -1.0) #=> -3.141592653589793
Math.atan2(-1.0, -1.0) #=> -2.356194490192345
Math.atan2(-1.0, 0.0) #=> -1.5707963267948966
Math.atan2(-1.0, 1.0) #=> -0.7853981633974483
Math.atan2(-0.0, 1.0) #=> -0.0
Math.atan2(0.0, 1.0) #=> 0.0
Math.atan2(1.0, 1.0) #=> 0.7853981633974483
Math.atan2(1.0, 0.0) #=> 1.5707963267948966
Math.atan2(1.0, -1.0) #=> 2.356194490192345
Math.atan2(0.0, -1.0) #=> 3.141592653589793
Math.atan2(INFINITY, INFINITY) #=> 0.7853981633974483
Math.atan2(INFINITY, -INFINITY) #=> 2.356194490192345
Math.atan2(-INFINITY, INFINITY) #=> -0.7853981633974483
Math.atan2(-INFINITY, -INFINITY) #=> -2.356194490192345

 static VALUE
math_atan2(VALUE unused_obj, VALUE y, VALUE x)
{
 double dx, dy;
 dx = Get_Double(x);
 dy = Get_Double(y);
 if (dx == 0.0 && dy == 0.0) {
 if (!signbit(dx))
 return DBL2NUM(dy);
 if (!signbit(dy))
 return DBL2NUM(M_PI);
 return DBL2NUM(-M_PI);
 }
#ifndef ATAN2_INF_C99
 if (isinf(dx) && isinf(dy)) {
 /* optimization for FLONUM */
 if (dx < 0.0) {
 const double dz = (3.0 * M_PI / 4.0);
 return (dy < 0.0) ? DBL2NUM(-dz) : DBL2NUM(dz);
 }
 else {
 const double dz = (M_PI / 4.0);
 return (dy < 0.0) ? DBL2NUM(-dz) : DBL2NUM(dz);
 }
 }
#endif
 return DBL2NUM(atan2(dy, dx));
}
 

Computes the inverse hyperbolic tangent of x.

Domain: (-1, 1)

Codomain: (-INFINITY, INFINITY)

Math.atanh(1) #=> Infinity

 static VALUE
math_atanh(VALUE unused_obj, VALUE x)
{
 double d;
 d = Get_Double(x);
 /* check for domain error */
 if (d < -1.0 || +1.0 < d) domain_error("atanh");
 /* check for pole error */
 if (d == -1.0) return DBL2NUM(-HUGE_VAL);
 if (d == +1.0) return DBL2NUM(+HUGE_VAL);
 return DBL2NUM(atanh(d));
}
 

Returns the cube root of x.

Domain: (-INFINITY, INFINITY)

Codomain: (-INFINITY, INFINITY)

-9.upto(9) {|x|
 p [x, Math.cbrt(x), Math.cbrt(x)**3]
}
#=> [-9, -2.0800838230519, -9.0]
# [-8, -2.0, -8.0]
# [-7, -1.91293118277239, -7.0]
# [-6, -1.81712059283214, -6.0]
# [-5, -1.7099759466767, -5.0]
# [-4, -1.5874010519682, -4.0]
# [-3, -1.44224957030741, -3.0]
# [-2, -1.25992104989487, -2.0]
# [-1, -1.0, -1.0]
# [0, 0.0, 0.0]
# [1, 1.0, 1.0]
# [2, 1.25992104989487, 2.0]
# [3, 1.44224957030741, 3.0]
# [4, 1.5874010519682, 4.0]
# [5, 1.7099759466767, 5.0]
# [6, 1.81712059283214, 6.0]
# [7, 1.91293118277239, 7.0]
# [8, 2.0, 8.0]
# [9, 2.0800838230519, 9.0]

 static VALUE
math_cbrt(VALUE unused_obj, VALUE x)
{
 double f = Get_Double(x);
 double r = cbrt(f);
#if defined __GLIBC__
 if (isfinite(r)) {
 r = (2.0 * r + (f / r / r)) / 3.0;
 }
#endif
 return DBL2NUM(r);
}
 

Computes the cosine of x (expressed in radians). Returns a Float in the range -1.0..1.0.

Domain: (-INFINITY, INFINITY)

Codomain: [-1, 1]

Math.cos(Math::PI) #=> -1.0

 static VALUE
math_cos(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(cos(Get_Double(x)));
}
 

Computes the hyperbolic cosine of x (expressed in radians).

Domain: (-INFINITY, INFINITY)

Codomain: [1, INFINITY)

Math.cosh(0) #=> 1.0

 static VALUE
math_cosh(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(cosh(Get_Double(x)));
}
 

Calculates the error function of x.

Domain: (-INFINITY, INFINITY)

Codomain: (-1, 1)

Math.erf(0) #=> 0.0

 static VALUE
math_erf(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(erf(Get_Double(x)));
}
 

Calculates the complementary error function of x.

Domain: (-INFINITY, INFINITY)

Codomain: (0, 2)

Math.erfc(0) #=> 1.0

 static VALUE
math_erfc(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(erfc(Get_Double(x)));
}
 

Returns e**x.

Domain: (-INFINITY, INFINITY)

Codomain: (0, INFINITY)

Math.exp(0) #=> 1.0
Math.exp(1) #=> 2.718281828459045
Math.exp(1.5) #=> 4.4816890703380645

 static VALUE
math_exp(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(exp(Get_Double(x)));
}
 

Returns a two-element array containing the normalized fraction (a Float) and exponent (an Integer) of x.

fraction, exponent = Math.frexp(1234) #=> [0.6025390625, 11]
fraction * 2**exponent #=> 1234.0

 static VALUE
math_frexp(VALUE unused_obj, VALUE x)
{
 double d;
 int exp;
 d = frexp(Get_Double(x), &exp);
 return rb_assoc_new(DBL2NUM(d), INT2NUM(exp));
}
 

Calculates the gamma function of x.

Note that gamma(n) is same as fact(n-1) for integer n > 0. However gamma(n) returns float and can be an approximation.

def fact(n) (1..n).inject(1) {|r,i| r*i } end
1.upto(26) {|i| p [i, Math.gamma(i), fact(i-1)] }
#=> [1, 1.0, 1]
# [2, 1.0, 1]
# [3, 2.0, 2]
# [4, 6.0, 6]
# [5, 24.0, 24]
# [6, 120.0, 120]
# [7, 720.0, 720]
# [8, 5040.0, 5040]
# [9, 40320.0, 40320]
# [10, 362880.0, 362880]
# [11, 3628800.0, 3628800]
# [12, 39916800.0, 39916800]
# [13, 479001600.0, 479001600]
# [14, 6227020800.0, 6227020800]
# [15, 87178291200.0, 87178291200]
# [16, 1307674368000.0, 1307674368000]
# [17, 20922789888000.0, 20922789888000]
# [18, 355687428096000.0, 355687428096000]
# [19, 6.402373705728e+15, 6402373705728000]
# [20, 1.21645100408832e+17, 121645100408832000]
# [21, 2.43290200817664e+18, 2432902008176640000]
# [22, 5.109094217170944e+19, 51090942171709440000]
# [23, 1.1240007277776077e+21, 1124000727777607680000]
# [24, 2.5852016738885062e+22, 25852016738884976640000]
# [25, 6.204484017332391e+23, 620448401733239439360000]
# [26, 1.5511210043330954e+25, 15511210043330985984000000]

 static VALUE
math_gamma(VALUE unused_obj, VALUE x)
{
 static const double fact_table[] = {
 /* fact(0) */ 1.0,
 /* fact(1) */ 1.0,
 /* fact(2) */ 2.0,
 /* fact(3) */ 6.0,
 /* fact(4) */ 24.0,
 /* fact(5) */ 120.0,
 /* fact(6) */ 720.0,
 /* fact(7) */ 5040.0,
 /* fact(8) */ 40320.0,
 /* fact(9) */ 362880.0,
 /* fact(10) */ 3628800.0,
 /* fact(11) */ 39916800.0,
 /* fact(12) */ 479001600.0,
 /* fact(13) */ 6227020800.0,
 /* fact(14) */ 87178291200.0,
 /* fact(15) */ 1307674368000.0,
 /* fact(16) */ 20922789888000.0,
 /* fact(17) */ 355687428096000.0,
 /* fact(18) */ 6402373705728000.0,
 /* fact(19) */ 121645100408832000.0,
 /* fact(20) */ 2432902008176640000.0,
 /* fact(21) */ 51090942171709440000.0,
 /* fact(22) */ 1124000727777607680000.0,
 /* fact(23)=25852016738884976640000 needs 56bit mantissa which is
 * impossible to represent exactly in IEEE 754 double which have
 * 53bit mantissa. */
 };
 enum {NFACT_TABLE = numberof(fact_table)};
 double d;
 d = Get_Double(x);
 /* check for domain error */
 if (isinf(d)) {
 if (signbit(d)) domain_error("gamma");
 return DBL2NUM(HUGE_VAL);
 }
 if (d == 0.0) {
 return signbit(d) ? DBL2NUM(-HUGE_VAL) : DBL2NUM(HUGE_VAL);
 }
 if (d == floor(d)) {
 if (d < 0.0) domain_error("gamma");
 if (1.0 <= d && d <= (double)NFACT_TABLE) {
 return DBL2NUM(fact_table[(int)d - 1]);
 }
 }
 return DBL2NUM(tgamma(d));
}
 

Returns sqrt(x**2 + y**2), the hypotenuse of a right-angled triangle with sides x and y.

Math.hypot(3, 4) #=> 5.0

 static VALUE
math_hypot(VALUE unused_obj, VALUE x, VALUE y)
{
 return DBL2NUM(hypot(Get_Double(x), Get_Double(y)));
}
 

Returns the value of fraction*(2**exponent).

fraction, exponent = Math.frexp(1234)
Math.ldexp(fraction, exponent) #=> 1234.0

 static VALUE
math_ldexp(VALUE unused_obj, VALUE x, VALUE n)
{
 return DBL2NUM(ldexp(Get_Double(x), NUM2INT(n)));
}
 

Calculates the logarithmic gamma of x and the sign of gamma of x.

::lgamma is same as

[Math.log(Math.gamma(x).abs), Math.gamma(x) < 0 ? -1 : 1]

but avoid overflow by ::gamma for large x.

Math.lgamma(0) #=> [Infinity, 1]

 static VALUE
math_lgamma(VALUE unused_obj, VALUE x)
{
 double d;
 int sign=1;
 VALUE v;
 d = Get_Double(x);
 /* check for domain error */
 if (isinf(d)) {
 if (signbit(d)) domain_error("lgamma");
 return rb_assoc_new(DBL2NUM(HUGE_VAL), INT2FIX(1));
 }
 if (d == 0.0) {
 VALUE vsign = signbit(d) ? INT2FIX(-1) : INT2FIX(+1);
 return rb_assoc_new(DBL2NUM(HUGE_VAL), vsign);
 }
 v = DBL2NUM(lgamma_r(d, &sign));
 return rb_assoc_new(v, INT2FIX(sign));
}
 

Returns the base 10 logarithm of x.

Domain: (0, INFINITY)

Codomain: (-INFINITY, INFINITY)

Math.log10(1) #=> 0.0
Math.log10(10) #=> 1.0
Math.log10(10**100) #=> 100.0

 static VALUE
math_log10(VALUE unused_obj, VALUE x)
{
 size_t numbits;
 double d = get_double_rshift(x, &numbits);
 /* check for domain error */
 if (d < 0.0) domain_error("log10");
 /* check for pole error */
 if (d == 0.0) return DBL2NUM(-HUGE_VAL);
 return DBL2NUM(log10(d) + numbits * log10(2)); /* log10(d * 2 ** numbits) */
}
 

Returns the base 2 logarithm of x.

Domain: (0, INFINITY)

Codomain: (-INFINITY, INFINITY)

Math.log2(1) #=> 0.0
Math.log2(2) #=> 1.0
Math.log2(32768) #=> 15.0
Math.log2(65536) #=> 16.0

 static VALUE
math_log2(VALUE unused_obj, VALUE x)
{
 size_t numbits;
 double d = get_double_rshift(x, &numbits);
 /* check for domain error */
 if (d < 0.0) domain_error("log2");
 /* check for pole error */
 if (d == 0.0) return DBL2NUM(-HUGE_VAL);
 return DBL2NUM(log2(d) + numbits); /* log2(d * 2 ** numbits) */
}
 

Computes the sine of x (expressed in radians). Returns a Float in the range -1.0..1.0.

Domain: (-INFINITY, INFINITY)

Codomain: [-1, 1]

Math.sin(Math::PI/2) #=> 1.0

 static VALUE
math_sin(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(sin(Get_Double(x)));
}
 

Computes the hyperbolic sine of x (expressed in radians).

Domain: (-INFINITY, INFINITY)

Codomain: (-INFINITY, INFINITY)

Math.sinh(0) #=> 0.0

 static VALUE
math_sinh(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(sinh(Get_Double(x)));
}
 

Returns the non-negative square root of x.

Domain: [0, INFINITY)

Codomain:[0, INFINITY)

0.upto(10) {|x|
 p [x, Math.sqrt(x), Math.sqrt(x)**2]
}
#=> [0, 0.0, 0.0]
# [1, 1.0, 1.0]
# [2, 1.4142135623731, 2.0]
# [3, 1.73205080756888, 3.0]
# [4, 2.0, 4.0]
# [5, 2.23606797749979, 5.0]
# [6, 2.44948974278318, 6.0]
# [7, 2.64575131106459, 7.0]
# [8, 2.82842712474619, 8.0]
# [9, 3.0, 9.0]
# [10, 3.16227766016838, 10.0]

Note that the limited precision of floating point arithmetic might lead to surprising results:

Math.sqrt(10**46).to_i #=> 99999999999999991611392 (!)

See also BigDecimal#sqrt and Integer.sqrt.

 static VALUE
math_sqrt(VALUE unused_obj, VALUE x)
{
 return rb_math_sqrt(x);
}
 

Computes the tangent of x (expressed in radians).

Domain: (-INFINITY, INFINITY)

Codomain: (-INFINITY, INFINITY)

Math.tan(0) #=> 0.0

 static VALUE
math_tan(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(tan(Get_Double(x)));
}
 

Computes the hyperbolic tangent of x (expressed in radians).

Domain: (-INFINITY, INFINITY)

Codomain: (-1, 1)

Math.tanh(0) #=> 0.0

 static VALUE
math_tanh(VALUE unused_obj, VALUE x)
{
 return DBL2NUM(tanh(Get_Double(x)));
}