From 6bf4b90c90f15f4ab60833bddf5b5756d1a6b1f6 Mon Sep 17 00:00:00 2001
From: Elizabeth Alexander Hunt <me@liz.coffee>
Date: Thu, 2 Jul 2026 11:55:17 -0700
Subject: Init

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+% Created 2023-11-01 Wed 20:49
+% Intended LaTeX compiler: pdflatex
+\documentclass[11pt]{article}
+\usepackage[utf8]{inputenc}
+\usepackage[T1]{fontenc}
+\usepackage{graphicx}
+\usepackage{longtable}
+\usepackage{wrapfig}
+\usepackage{rotating}
+\usepackage[normalem]{ulem}
+\usepackage{amsmath}
+\usepackage{amssymb}
+\usepackage{capt-of}
+\usepackage{hyperref}
+\notindent \notag  \usepackage{amsmath} \usepackage[a4paper,margin=1in,portrait]{geometry}
+\author{Elizabeth Hunt}
+\date{\today}
+\title{Homework 5}
+\hypersetup{
+ pdfauthor={Elizabeth Hunt},
+ pdftitle={Homework 5},
+ pdfkeywords={},
+ pdfsubject={},
+ pdfcreator={Emacs 28.2 (Org mode 9.7-pre)}, 
+ pdflang={English}}
+\begin{document}
+
+\maketitle
+\setlength\parindent{0pt}
+
+\section{Question One}
+\label{sec:org4e80298}
+See LIZFCM \(\rightarrow\) Matrix Routines \(\rightarrow\) \texttt{lu decomp} \& \texttt{bsubst}.
+
+The test \texttt{UTEST(matrix, lu\_decomp)} is a unit test for the \texttt{lu\_decomp} routine,
+and \texttt{UTEST(matrix, bsubst)} verifies back substitution on an upper triangular
+3 \texttimes{} 3 matrix with a known solution that can be verified manually.
+
+Both can be found in \texttt{tests/matrix.t.c}.
+
+\section{Question Two}
+\label{sec:orga73d05c}
+Unless the following are met, the resulting solution will be garbage.
+
+\begin{enumerate}
+\item The matrix \(U\) must be not be singular.
+\item \(U\) must be square (or it will fail the \texttt{assert}).
+\item The system created by \(Ux = b\) must be consistent.
+\item \(U\) is (quite obviously) in upper-triangular form.
+\end{enumerate}
+
+Thus, the actual calculation performing the \(LU\) decomposition
+(in \texttt{lu\_decomp}) does a sanity
+check for 1-3 will fail an assert, should a point along the diagonal (pivot) be
+zero, or the matrix be non-factorable.
+
+\section{Question Three}
+\label{sec:org35163c5}
+See LIZFCM \(\rightarrow\) Matrix Routines \(\rightarrow\) \texttt{fsubst}.
+
+\texttt{UTEST(matrix, fsubst)} verifies forward substitution on a lower triangular 3 \texttimes{} 3
+matrix with a known solution that can be verified manually.
+
+\section{Question Four}
+\label{sec:org79d9061}
+
+See LIZFCM \(\rightarrow\) Matrix Routines \(\rightarrow\) \texttt{gaussian\_elimination} and \texttt{solve\_gaussian\_elimination}.
+
+\section{Question Five}
+\label{sec:orgc6ac464}
+See LIZFCM \(\rightarrow\) Matrix Routines \(\rightarrow\) \texttt{m\_dot\_v}, and the \texttt{UTEST(matrix, m\_dot\_v)} in
+\texttt{tests/matrix.t.c}.
+
+\section{Question Six}
+\label{sec:org66fedab}
+See \texttt{UTEST(matrix, solve\_gaussian\_elimination)} in \texttt{tests/matrix.t.c}, which generates a diagonally dominant 10 \texttimes{} 10 matrix
+and shows that the solution is consistent with the initial matrix, according to the steps given. Then,
+we do a dot product between each row of the diagonally dominant matrix and the solution vector to ensure
+it is near equivalent to the input vector.
+
+\section{Question Seven}
+\label{sec:org6897ff2}
+See \texttt{UTEST(matrix, solve\_matrix\_lu\_bsubst)} which does the same test in Question Six with the solution according to
+\texttt{solve\_matrix\_lu\_bsubst} as shown in the Software Manual.
+
+\section{Question Eight}
+\label{sec:org5d529dd}
+No, since the time complexity for Gaussian Elimination is always less than that of the LU factorization solution by \(O(n^2)\) operations
+(in LU factorization we perform both backwards and forwards substitutions proceeding the LU decomp, in Gaussian Elimination we only need
+back substitution).
+
+\section{Question Nine, Ten}
+\label{sec:org0fb8e09}
+See LIZFCM Software manual and shared library in \texttt{dist} after compiling.
+\end{document}
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