Module: BigMath

Defined in:
lib/extensions/bigdecimal/bigdecimal/math.rb

Overview

– Contents:

sqrt(x, prec)
sin (x, prec)
cos (x, prec)
atan(x, prec)  Note: |x|<1, x=0.9999 may not converge.
PI  (prec)
E   (prec) == exp(1.0,prec)

where:

x    ... BigDecimal number to be computed.
         |x| must be small enough to get convergence.
prec ... Number of digits to be obtained.

++

Provides mathematical functions.

Example:

require "bigdecimal/math"

include BigMath

a = BigDecimal((PI(100)/2).to_s)
puts sin(a,100) # => 0.10000000000000000000......E1

Class Method Summary collapse

Class Method Details

.atan(x, prec) ⇒ Object

call-seq:

atan(decimal, numeric) -> BigDecimal

Computes the arctangent of decimal to the specified number of digits of precision, numeric.

If decimal is NaN, returns NaN.

BigMath.atan(BigDecimal.new('-1'), 16).to_s
#=> "-0.785398163397448309615660845819878471907514682065E0"

Raises:

  • (ArgumentError) 


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# File 'lib/extensions/bigdecimal/bigdecimal/math.rb', line 146

def atan(x, prec)
  raise ArgumentError, "Zero or negative precision for atan" if prec <= 0
  return BigDecimal("NaN") if x.nan?
  pi = PI(prec)
  x = -x if neg = x < 0
  return pi.div(neg ? -2 : 2, prec) if x.infinite?
  return pi / (neg ? -4 : 4) if x.round(prec) == 1
  x = BigDecimal("1").div(x, prec) if inv = x > 1
  x = (-1 + sqrt(1 + x**2, prec))/x if dbl = x > 0.5
  n    = prec + BigDecimal.double_fig
  y = x
  d = y
  t = x
  r = BigDecimal("3")
  x2 = x.mult(x,n)
  while d.nonzero? && ((m = n - (y.exponent - d.exponent).abs) > 0)
    m = BigDecimal.double_fig if m < BigDecimal.double_fig
    t = -t.mult(x2,n)
    d = t.div(r,m)
    y += d
    r += 2
  end
  y *= 2 if dbl
  y = pi / 2 - y if inv
  y = -y if neg
  y
end

.cos(x, prec) ⇒ Object

call-seq:

cos(decimal, numeric) -> BigDecimal

Computes the cosine of decimal to the specified number of digits of precision, numeric.

If decimal is Infinity or NaN, returns NaN.

BigMath.cos(BigMath.PI(4), 16).to_s
#=> "-0.999999999999999999999999999999856613163740061349E0"

Raises:

  • (ArgumentError) 


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# File 'lib/extensions/bigdecimal/bigdecimal/math.rb', line 102

def cos(x, prec)
  raise ArgumentError, "Zero or negative precision for cos" if prec <= 0
  return BigDecimal("NaN") if x.infinite? || x.nan?
  n    = prec + BigDecimal.double_fig
  one  = BigDecimal("1")
  two  = BigDecimal("2")
  x = -x if x < 0
  if x > (twopi = two * BigMath.PI(prec))
    if x > 30
      x %= twopi
    else
      x -= twopi while x > twopi
    end
  end
  x1 = one
  x2 = x.mult(x,n)
  sign = 1
  y = one
  d = y
  i = BigDecimal("0")
  z = one
  while d.nonzero? && ((m = n - (y.exponent - d.exponent).abs) > 0)
    m = BigDecimal.double_fig if m < BigDecimal.double_fig
    sign = -sign
    x1  = x2.mult(x1,n)
    i  += two
    z  *= (i-one) * i
    d   = sign * x1.div(z,m)
    y  += d
  end
  y
end

.E(prec) ⇒ Object

call-seq:

E(numeric) -> BigDecimal

Computes e (the base of natural logarithms) to the specified number of digits of precision, numeric.

BigMath.E(10).to_s
#=> "0.271828182845904523536028752390026306410273E1"

Raises:

  • (ArgumentError) 


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# File 'lib/extensions/bigdecimal/bigdecimal/math.rb', line 228

def E(prec)
  raise ArgumentError, "Zero or negative precision for E" if prec <= 0
  BigMath.exp(1, prec)
end

.PI(prec) ⇒ Object

call-seq:

PI(numeric) -> BigDecimal

Computes the value of pi to the specified number of digits of precision, numeric.

BigMath.PI(10).to_s
#=> "0.3141592653589793238462643388813853786957412E1"

Raises:

  • (ArgumentError) 


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# File 'lib/extensions/bigdecimal/bigdecimal/math.rb', line 183

def PI(prec)
  raise ArgumentError, "Zero or negative precision for PI" if prec <= 0
  n      = prec + BigDecimal.double_fig
  zero   = BigDecimal("0")
  one    = BigDecimal("1")
  two    = BigDecimal("2")

  m25    = BigDecimal("-0.04")
  m57121 = BigDecimal("-57121")

  pi     = zero

  d = one
  k = one
  t = BigDecimal("-80")
  while d.nonzero? && ((m = n - (pi.exponent - d.exponent).abs) > 0)
    m = BigDecimal.double_fig if m < BigDecimal.double_fig
    t   = t*m25
    d   = t.div(k,m)
    k   = k+two
    pi  = pi + d
  end

  d = one
  k = one
  t = BigDecimal("956")
  while d.nonzero? && ((m = n - (pi.exponent - d.exponent).abs) > 0)
    m = BigDecimal.double_fig if m < BigDecimal.double_fig
    t   = t.div(m57121,n)
    d   = t.div(k,m)
    pi  = pi + d
    k   = k+two
  end
  pi
end

.sin(x, prec) ⇒ Object

call-seq:

sin(decimal, numeric) -> BigDecimal

Computes the sine of decimal to the specified number of digits of precision, numeric.

If decimal is Infinity or NaN, returns NaN.

BigMath.sin(BigMath.PI(5)/4, 5).to_s
#=> "0.70710678118654752440082036563292800375E0"

Raises:

  • (ArgumentError) 


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# File 'lib/extensions/bigdecimal/bigdecimal/math.rb', line 58

def sin(x, prec)
  raise ArgumentError, "Zero or negative precision for sin" if prec <= 0
  return BigDecimal("NaN") if x.infinite? || x.nan?
  n    = prec + BigDecimal.double_fig
  one  = BigDecimal("1")
  two  = BigDecimal("2")
  x = -x if neg = x < 0
  if x > (twopi = two * BigMath.PI(prec))
    if x > 30
      x %= twopi
    else
      x -= twopi while x > twopi
    end
  end
  x1   = x
  x2   = x.mult(x,n)
  sign = 1
  y    = x
  d    = y
  i    = one
  z    = one
  while d.nonzero? && ((m = n - (y.exponent - d.exponent).abs) > 0)
    m = BigDecimal.double_fig if m < BigDecimal.double_fig
    sign = -sign
    x1  = x2.mult(x1,n)
    i  += two
    z  *= (i-one) * i
    d   = sign * x1.div(z,m)
    y  += d
  end
  neg ? -y : y
end

.sqrt(x, prec) ⇒ Object

call-seq:

sqrt(decimal, numeric) -> BigDecimal

Computes the square root of decimal to the specified number of digits of precision, numeric.

BigMath.sqrt(BigDecimal.new('2'), 16).to_s
#=> "0.1414213562373095048801688724E1"



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# File 'lib/extensions/bigdecimal/bigdecimal/math.rb', line 43

def sqrt(x, prec)
  x.sqrt(prec)
end