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#!/usr/local/bin/ruby
#
# 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.
#
require "bigdecimal"
require "ludcmp"
include LUSolve
def rd_order
printf("Number of equations ?")
n = gets().chomp.to_i
end
zero = BigDecimal::new("0.0")
one = BigDecimal::new("1.0")
while (n=rd_order())>0
a = []
as= []
b = []
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 = gets
a <<=BigDecimal::new(s);
as<<=BigDecimal::new(s);
end
printf("Contatant vector element b[%d] ? ",i);b<<=BigDecimal::new(gets);
end
printf "ANS="
x = lusolve(a,b,ludecomp(a,n,zero,one),zero)
p x
printf "A*x-b\n"
for i in 0...n do
s = zero
for j in 0...n do
s = s + as[i*n+j]*x[j]
end
p s-b[i]
end
end
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