#!/usr/local/bin/ruby
# frozen_string_literal: false
#
# linear.rb
#
# Solves linear equation system(A*x = b) by LU decomposition method.
# where A is a coefficient matrix,x is an answer vector,b is a constant vector.
#
# USAGE:
# ruby linear.rb [input file solved]
#
# :stopdoc:
require "bigdecimal"
require "bigdecimal/ludcmp"
#
# NOTE:
# Change following BigDecimal.limit() if needed.
BigDecimal.limit(100)
#
include LUSolve
def rd_order(na)
printf("Number of equations ?") if(na <= 0)
n = ARGF.gets().to_i
end
na = ARGV.size
zero = BigDecimal("0.0")
one = BigDecimal("1.0")
while (n=rd_order(na))>0
a = []
as= []
b = []
if na <= 0
# Read data from console.
printf("\nEnter coefficient matrix element A[i,j]\n")
for i in 0...n do
for j in 0...n do
printf("A[%d,%d]? ",i,j); s = ARGF.gets
a << BigDecimal(s)
as << BigDecimal(s)
end
printf("Contatant vector element b[%d] ? ",i)
b << BigDecimal(ARGF.gets)
end
else
# Read data from specified file.
printf("Coefficient matrix and constant vector.\n")
for i in 0...n do
s = ARGF.gets
printf("%d) %s",i,s)
s = s.split
for j in 0...n do
a << BigDecimal(s[j])
as << BigDecimal(s[j])
end
b << BigDecimal(s[n])
end
end
x = lusolve(a,b,ludecomp(a,n,zero,one),zero)
printf("Answer(x[i] & (A*x-b)[i]) follows\n")
for i in 0...n do
printf("x[%d]=%s ",i,x[i].to_s)
s = zero
for j in 0...n do
s = s + as[i*n+j]*x[j]
end
printf(" & %s\n",(s-b[i]).to_s)
end
end
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