= Examples

== Example 1: Initialization
You must require 'mpfr' to use MPFR.
And you set the default precision by MPFR.set_default_prec.
To make an instance of MPFR, you can use MPFR.new or MPFR methods.
MPFR.new and MPFR have the same arguments.
First argument is a number which is Fixnum, Bignum, Float, String, or MPFR.
The following two optional arguments are rounding mode and precision.

 require "mpfr"
 MPFR.set_default_prec(100)
 
 a = MPFR(3.3)       # or MPFR.new(3.3)
 b = MPFR('2.2')     # or MPFR.new('2.2')
 puts (a + b).to_s   # => 5.4999999999999998223643160599724e+00
 puts (a - b).to_s   # => 1.0999999999999998223643160599743e+00
 puts (a * b).to_s   # => 7.2599999999999996092014953319487e+00
 puts (a / b).to_s   # => 1.4999999999999999192565072999879e+00
 
 c = MPFR('4.321', MPFR::RNDU)
 d = MPFR('4.321', MPFR::RNDD)
 c > d    # => true
 
 e = MPFR('4.321', MPFR::RNDN, 256)
 e.prec   # => 256
 d.prec   # => 100

== Example 2: Convertion to String
You can use MPFR#to_s and MPFR#to_strf to convert
an instance of MPFR to String.
These methods use function mpfr_asprintf.
MPFR#to_s convert an instance to string by mpfr_asprintf(str, "%.Re", self);
If you execute MPFR#to_strf(format), you get string converted
by mpfr_asprintf(str, format, self);

 require "mpfr"
 MPFR.set_default_prec(128)
 
 a = MPFR('0.3')
 puts a.to_s              # => 3.000000000000000000000000000000000000006e-01
 puts a.to_strf("%.20Re") # => 3.00000000000000000000e-01
 puts a.to_strf("%.20RE") # => 3.00000000000000000000E-01
 puts a.to_strf("%.20Rf") # => 0.30000000000000000000

== Example 3: Special Functions
Special functions of MPFR is collected in MPFR::Math.
MPFR::Math.func corresponds to mpfr_func in C language.
For example, you can use MPFR::Math.log to use mpfr_log.
Method of MPFR::Math is two optional arguments; rounding mode and percision.

 require "mpfr"
 MPFR.set_default_prec(128)
 
 MPFR::Math.log('0.3') # => -1.203972804325935992622746217761838502954e+00
 MPFR::Math.sin(1.23)  # => 9.424888019316975040865688397571963882576e-01
 
 a = MPFR::Math.sin(1.23, MPFR::RNDU) # => 9.424888019316975040865688397571963882576e-01
 b = MPFR::Math.sin(1.23, MPFR::RNDD) # => 9.424888019316975040865688397571963882547e-01
 a > b   # => true
 
 e = MPFR::Math.sin(1.23, MPFR::RNDD, 256)
 e.get_prec   # => 256