Module | BigMath
In: | bigdecimal/lib/bigdecimal/math.rb

Contents:

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

Usage:

      require "bigdecimal"
      require "bigdecimal/math.rb"
      include BigMath
      a = BigDecimal((PI(100)/2).to_s)
      puts sin(a,100) # => 0.10000000000000000000......E1

### Methods

E PI atan cos exp log sin sqrt

### Public Instance methods

E(prec)

[Source]

    # File bigdecimal/lib/bigdecimal/math.rb, line 179
      def E(prec)
        raise ArgumentError, "Zero or negative precision for E" if prec <= 0
        n    = prec + BigDecimal.double_fig
        one  = BigDecimal("1")
        y  = one
        d  = y
        z  = one
        i  = 0
        while d.nonzero? && ((m = n - (y.exponent - d.exponent).abs) > 0)
          m = BigDecimal.double_fig if m < BigDecimal.double_fig
          i += 1
          z *= i
          d  = one.div(z,m)
          y += d
        end
        y
      end

PI(prec)

[Source]

    # File bigdecimal/lib/bigdecimal/math.rb, line 141
      def PI(prec)
        raise ArgumentError, "Zero or negative argument 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
        w = 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
        w = 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

atan(x, prec)

[Source]

    # File bigdecimal/lib/bigdecimal/math.rb, line 79
      def atan(x, prec)
        raise ArgumentError, "Zero or negative precision for atan" if prec <= 0
        return BigDecimal("NaN") if x.infinite? || x.nan?
        raise ArgumentError, "x.abs must be less than 1.0" if x.abs>=1
        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
      end

cos(x, prec)

[Source]

    # File bigdecimal/lib/bigdecimal/math.rb, line 54
      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")
        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

exp(x, prec)

[Source]

    # File bigdecimal/lib/bigdecimal/math.rb, line 99
      def exp(x, prec)
        raise ArgumentError, "Zero or negative precision for exp" if prec <= 0
        return BigDecimal("NaN") if x.infinite? || x.nan?
        n    = prec + BigDecimal.double_fig
        one  = BigDecimal("1")
        x1 = one
        y  = one
        d  = y
        z  = one
        i  = 0
        while d.nonzero? && ((m = n - (y.exponent - d.exponent).abs) > 0)
          m = BigDecimal.double_fig if m < BigDecimal.double_fig
          x1  = x1.mult(x,n)
          i += 1
          z *= i
          d  = x1.div(z,m)
          y += d
        end
        y
      end

log(x, prec)

[Source]

    # File bigdecimal/lib/bigdecimal/math.rb, line 120
      def log(x, prec)
        raise ArgumentError, "Zero or negative argument for log" if x <= 0 || prec <= 0
        return x if x.infinite? || x.nan?
        one = BigDecimal("1")
        two = BigDecimal("2")
        n  = prec + BigDecimal.double_fig
        x  = (x - one).div(x + one,n)
        x2 = x.mult(x,n)
        y  = x
        d  = y
        i = one
        while d.nonzero? && ((m = n - (y.exponent - d.exponent).abs) > 0)
          m = BigDecimal.double_fig if m < BigDecimal.double_fig
          x  = x2.mult(x,n)
          i += two
          d  = x.div(i,m)
          y += d
        end
        y*two
      end

sin(x, prec)

[Source]

    # File bigdecimal/lib/bigdecimal/math.rb, line 29
      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")
        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
        y
      end

sqrt(x,prec)

[Source]

    # File bigdecimal/lib/bigdecimal/math.rb, line 25
      def sqrt(x,prec)
        x.sqrt(prec)
      end

[Validate]