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I am learning about the linear system of Diophantine equations. I have noticed that the solution structure of the Diophantine equation is quite similar to the general system of linear equations. It is $S=x_0+F$, where $x_0$ is a partial solution and $F$ is the solution set of the corresponding homogeneous Diophantine linear system, $F$ is the submodule of $\mathbb{Z}$-module $\mathbb{Z^n}$. But in the general system of equations, $F$ is a subspace of the vector space $K^n$.
So, is the proof for the root structure theorem of the linear system of the Diophantine equations similar to the general system of equations? If it is different, can someone give me a tutorial to proof, please?

My proof for the structure of the solution set of a general linear equation system:

Theorem: If the general system of linear equations $\left\{\begin{array}\ a_{11}x_1+\cdot+a_{1n}x_n=b_1\\ \vdots\\ a_{m1}x_1+\cdots+a_{mn}x_n=b_m \end{array}\right. (*) $ has a solution, then the solution set $S$ has the form $$S=x_0+F,$$ where $x_0$ is a partial solution of $(*)$ and $F$ is the solution set of the corresponding homogeneous system of linear equations, $F$ is a subspace of $K^n$.

Proof: The system $(*)$ can be written as $f(x)=b$. We have $f(x_0)=b$ and $F=Ker(f)$. Suppose that $x\in K^n$ is any solution of $(*)$, then $f(x)=b$. This implies $f(x-x_0)=0$. Hence $x-x_0\in Ker(f)=F$. Thus $x\in x_0+F$. Conversely, if $x=x_0+w$, for $w\in F$, then $$f(x)=f(x_0+w)=f(x_0)+f(w)=b+0=b.$$ Therefore $x$ is a solution of $(*)$. Hence $S=x_0+F$.

  • All you have to do is show that the difference between two solutions is a solution to the homogeneous system, no? – Gerry Myerson Apr 29 '22 at 04:06
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    The well-known form of the general solution (e.g. see here) holds for any linear system, something that will be abstracted when one studies linear algebra, modules, affine spaces, etc, but can still be comprehended easily at more elementary levels in concrete cases such as here. – Bill Dubuque Apr 29 '22 at 07:56

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