Continued fraction convergents: Difference between revisions
m (→{{header|Phix}}: removed r too) |
(julia example) |
||
Line 21: | Line 21: | ||
* [[Continued fraction/Arithmetic/Construct from rational number]] |
* [[Continued fraction/Arithmetic/Construct from rational number]] |
||
* [[Calkin-Wilf sequence]] |
* [[Calkin-Wilf sequence]] |
||
=={{header|Julia}}== |
|||
<syntaxhighlight lang="julia">function convergents(x::Real, maxcount::T) where T <: Integer |
|||
components = T[] |
|||
rationals = Rational{T}[] |
|||
for _ in 1:maxcount |
|||
fpart, ipart = modf(x) |
|||
push!(components, T(ipart)) |
|||
fpart == 0 && break |
|||
x = inv(fpart) |
|||
end |
|||
numa, denoma, numb, denomb = T(1), T(0), T(components[begin]), T(1) |
|||
push!(rationals, numb // denomb) |
|||
for comp in components[begin+1:end] |
|||
numa, denoma, numb, denomb = numb, denomb, numa + comp * numb, denoma + comp * denomb |
|||
push!(rationals, numb // denomb) |
|||
end |
|||
return rationals |
|||
end |
|||
const tests = [("415/93", 415//93), ("649/200", 649//200), ("sqrt(2)", sqrt(2)), |
|||
("sqrt(5)", sqrt(5)), ("golden ratio", (sqrt(5) + 1) / 2)] |
|||
println("The continued fraction convergents for the following (maximum 8 terms) are:") |
|||
for (s, x) in tests |
|||
println(lpad(s, 15), " = ", convergents(x, 8)) |
|||
end |
|||
</syntaxhighlight>{{out}} |
|||
<pre> |
|||
The continued fraction convergents for the following (maximum 8 terms) are: |
|||
415/93 = Rational{Int64}[4, 9//2, 58//13, 415//93] |
|||
649/200 = Rational{Int64}[3, 13//4, 159//49, 649//200] |
|||
sqrt(2) = Rational{Int64}[1, 3//2, 7//5, 17//12, 41//29, 99//70, 239//169, 577//408] |
|||
sqrt(5) = Rational{Int64}[2, 9//4, 38//17, 161//72, 682//305, 2889//1292, 12238//5473, 51841//23184] |
|||
golden ratio = Rational{Int64}[1, 2, 3//2, 5//3, 8//5, 13//8, 21//13, 34//21] |
|||
</pre> |
|||
=={{header|Phix}}== |
=={{header|Phix}}== |
Revision as of 07:54, 7 February 2024
Given a positive real number, if we truncate its continued fraction representation at a certain depth, we obtain a rational approximation to the real number. The sequence of successively better such approximations is its convergent sequence.
Problem:
- Given a positive rational number , specified by two positive integers , output its entire sequence of convergents.
- Given a quadratic real number , specified by integers , where is not a perfect square, output the first convergents when given a positive number .
The output format can be whatever is necessary to represent rational numbers, but it probably should be a 2-tuple of integers.
For example, given , since
A simple check is to do this for the golden ratio , that is, , which should output .
Print the results for 415/93, 649/200, , , and the golden ratio.
- References and related tasks
- Wikipedia: Continued fraction
- Continued fraction
- Continued fraction/Arithmetic
- Continued fraction/Arithmetic/Construct from rational number
- Calkin-Wilf sequence
Julia
function convergents(x::Real, maxcount::T) where T <: Integer
components = T[]
rationals = Rational{T}[]
for _ in 1:maxcount
fpart, ipart = modf(x)
push!(components, T(ipart))
fpart == 0 && break
x = inv(fpart)
end
numa, denoma, numb, denomb = T(1), T(0), T(components[begin]), T(1)
push!(rationals, numb // denomb)
for comp in components[begin+1:end]
numa, denoma, numb, denomb = numb, denomb, numa + comp * numb, denoma + comp * denomb
push!(rationals, numb // denomb)
end
return rationals
end
const tests = [("415/93", 415//93), ("649/200", 649//200), ("sqrt(2)", sqrt(2)),
("sqrt(5)", sqrt(5)), ("golden ratio", (sqrt(5) + 1) / 2)]
println("The continued fraction convergents for the following (maximum 8 terms) are:")
for (s, x) in tests
println(lpad(s, 15), " = ", convergents(x, 8))
end
- Output:
The continued fraction convergents for the following (maximum 8 terms) are: 415/93 = Rational{Int64}[4, 9//2, 58//13, 415//93] 649/200 = Rational{Int64}[3, 13//4, 159//49, 649//200] sqrt(2) = Rational{Int64}[1, 3//2, 7//5, 17//12, 41//29, 99//70, 239//169, 577//408] sqrt(5) = Rational{Int64}[2, 9//4, 38//17, 161//72, 682//305, 2889//1292, 12238//5473, 51841//23184] golden ratio = Rational{Int64}[1, 2, 3//2, 5//3, 8//5, 13//8, 21//13, 34//21]
Phix
with javascript_semantics
requires("1.0.5") -- mpq_get_d() added
include mpfr.e
procedure cfcRat(integer m, n)
sequence p = {mpq_init(0), mpq_init(1)},
q = {mpq_init(1), mpq_init(0)},
s = {{sprintf("= %d/%d =",{m,n}),m/n}}
mpq r = mpq_init_set_si(m, n),
rem = mpq_init_set(r)
while true do
mpq whole = mpq_init_set_si(trunc(mpq_get_d(rem)))
mpq {pn, qn, sn} = mpq_inits(3)
mpq_mul(pn,whole,p[-1])
mpq_add(pn,pn,p[-2])
mpq_mul(qn,whole,q[-1])
mpq_add(qn,qn,q[-2])
mpq_div(sn,pn,qn)
p &= pn
q &= qn
s &= {{mpq_get_str(sn),mpq_get_d(sn)}}
if mpq_cmp(r,sn)=0 then exit end if
mpq_sub(rem,rem,whole)
mpq_inv(rem,rem)
end while
printf(1,"%s\n",join(s,"\n",fmt:="%-11s = %f"))
end procedure
procedure cfcQuad(string d, atom v, integer a, b, m, n, k)
sequence p = {0, 1},
q = {1, 0},
s = {{sprintf("= %s =",d),v}}
atom rem = (sqrt(a)*b + m) / n
for i=1 to k do
integer whole = trunc(rem),
pn = whole * p[-1] + p[-2],
qn = whole * q[-1] + q[-2]
mpq sn = mpq_init_set_si(pn, qn)
p &= pn
q &= qn
s &= {{mpq_get_str(sn),mpq_get_d(sn)}}
rem = 1/(rem-whole)
end for
printf(1,"%s\n",join(s,"\n",fmt:="%-11s = %f"))
end procedure
cfcRat(415,93)
cfcRat(649,200)
cfcQuad("sqrt(2)",sqrt(2),2, 1, 0, 1, 8)
cfcQuad("sqrt(5)",sqrt(5),5, 1, 0, 1, 8)
cfcQuad("phi",(sqrt(5)+1)/2,5, 1, 1, 2, 8)
- Output:
= 415/93 = = 4.462366 4 = 4.000000 9/2 = 4.500000 58/13 = 4.461538 415/93 = 4.462366 = 649/200 = = 3.245000 3 = 3.000000 13/4 = 3.250000 159/49 = 3.244898 649/200 = 3.245000 = sqrt(2) = = 1.414214 1 = 1.000000 3/2 = 1.500000 7/5 = 1.400000 17/12 = 1.416667 41/29 = 1.413793 99/70 = 1.414286 239/169 = 1.414201 577/408 = 1.414216 = sqrt(5) = = 2.236068 2 = 2.000000 9/4 = 2.250000 38/17 = 2.235294 161/72 = 2.236111 682/305 = 2.236066 2889/1292 = 2.236068 12238/5473 = 2.236068 51841/23184 = 2.236068 = phi = = 1.618034 1 = 1.000000 2 = 2.000000 3/2 = 1.500000 5/3 = 1.666667 8/5 = 1.600000 13/8 = 1.625000 21/13 = 1.615385 34/21 = 1.619048
Wren
The following is loosely based on the Python code here. If a large number of terms were required for quadratic real numbers, then one might need to use 'arbitrary precision' arithmetic to minimize round-off errors when converting between floats and rationals.
import "./rat" for Rat
var cfcRat = Fn.new { |m, n|
var p = [0, 1]
var q = [1, 0]
var s = []
var r = Rat.new(m, n)
var rem = r
while (true) {
var whole = rem.truncate
var frac = rem.fraction
var pn = whole * p[-1] + p[-2]
var qn = whole * q[-1] + q[-2]
var sn = pn / qn
p.add(pn)
q.add(qn)
s.add(sn)
if (r == sn) break
rem = frac.inverse
}
return s
}
var cfcQuad = Fn.new { |a, b, m, n, k|
var p = [0, 1]
var q = [1, 0]
var s = []
var rem = (a.sqrt * b + m) / n
for (i in 1..k) {
var whole = rem.truncate
var frac = rem.fraction
var pn = whole * p[-1] + p[-2]
var qn = whole * q[-1] + q[-2]
var sn = Rat.new(pn, qn)
p.add(pn)
q.add(qn)
s.add(sn)
rem = 1 / frac
}
return s
}
System.print("The continued fraction convergents for the following (maximum 8 terms) are:")
System.print("415/93 = %(cfcRat.call(415, 93))")
System.print("649/200 = %(cfcRat.call(649, 200))")
System.print("√2 = %(cfcQuad.call(2, 1, 0, 1, 8))")
System.print("√5 = %(cfcQuad.call(5, 1, 0, 1, 8))")
System.print("phi = %(cfcQuad.call(5, 1, 1, 2, 8))")
- Output:
The continued fraction convergents for the following (maximum 8 terms) are: 415/93 = [4/1, 9/2, 58/13, 415/93] 649/200 = [3/1, 13/4, 159/49, 649/200] √2 = [1/1, 3/2, 7/5, 17/12, 41/29, 99/70, 239/169, 577/408] √5 = [2/1, 9/4, 38/17, 161/72, 682/305, 2889/1292, 12238/5473, 51841/23184] phi = [1/1, 2/1, 3/2, 5/3, 8/5, 13/8, 21/13, 34/21]