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Thomas algorithm implementation in Common Lisp #604

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Merged
merged 8 commits into from
Jul 7, 2020
Merged

Thomas algorithm implementation in Common Lisp #604

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7b5c628
Added a proof for the Euclidean Algorithm
Trashtalk217 May 31, 2019
131ae54
Revert "Added a proof for the Euclidean Algorithm"
Trashtalk217 May 31, 2019
0b2b247
First working version thomas algorithm in lisp.
Trashtalk217 Jun 1, 2019
d953323
Added lisp code to the .md file
Trashtalk217 Jun 1, 2019
ca3d80b
Minor changes to make the code shorter.
Trashtalk217 Jun 3, 2019
ffff663
fixed merge conflict
Trashtalk217 Jul 5, 2020
4aadc56
output is now floating point, function is non-destructive.
Trashtalk217 Jul 5, 2020
f4a5770
fixed the wrong test and added in a macro
Trashtalk217 Jul 6, 2020
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29 changes: 29 additions & 0 deletions contents/thomas_algorithm/code/clisp/thomas.lisp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
;;;; Thomas algorithm implementation in Common Lisp

(defun thomas (a b c d)
"Returns the solutions to a tri-diagonal matrix destructively"
(setf (svref c 0) (/ (svref c 0) (svref b 0)))
(setf (svref d 0) (/ (svref d 0) (svref b 0)))
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Same comment about the macro here. Give them good docstrings.


(loop
for i from 1 upto (1- (length a)) do
(setf
(svref c i)
(/ (svref c i) (- (svref b i) (* (svref a i) (svref c (1- i))))))
(setf
(svref d i)
(/
(- (svref d i) (* (svref a i) (svref d (1- i))))
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If you want to write a macro, (- (svref d i) (* (svref a i) (svref d (1- i)))) is probably the level of granularity that you want, with a separate macro for the 1+ version. Since you aren't shortening the code by using macros, make sure you use a descriptive macro name.

(- (svref b i) (* (svref a i) (svref c (1- i)))))))

(loop
for i from (- (length a) 2) downto 0 do
(decf (svref d i) (* (svref c i) (svref d (1+ i))))
finally (return d)))

(defvar diagonal-a #(0 2 3))
(defvar diagonal-b #(1 3 6))
(defvar diagonal-c #(4 5 0))
(defvar last-column #(7 5 3))

(print (thomas diagonal-a diagonal-b diagonal-c last-column))
2 changes: 2 additions & 0 deletions contents/thomas_algorithm/thomas_algorithm.md
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Expand Up @@ -127,6 +127,8 @@ You will find this algorithm implemented [in this project](https://scratch.mit.e
[import, lang:"crystal"](code/crystal/thomas.cr)
{% sample lang="kotlin" %}
[import, lang:"kotlin"](code/kotlin/thomas.kt)
{% sample lang="lisp" %}
[import, lang:"lisp"](code/clisp/thomas.lisp)
{% endmethod %}

<script>
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